Edge coated gaskets and method of making same

ABSTRACT

An edge coated gasket includes a base sheet made of compressible gasket material and having opposed faces and an interior edge surrounding and defining an aperture. An edge coating of polymer or other material is disposed on and seals the interior edge of the base sheet and may project beyond the facial planes of the base sheet to define protruding rims extending around the aperture. Face coatings may also be applied to one or more of the faces extending in relatively narrow strips around the aperture of the base sheet. When clamped between flange surfaces, the edge coating engages, conforms to, and seals against the flange surfaces to provide a seal against both interfacial and intersticial migration of fluid past the gasket. At the same time, the inherently good compression failure resistance of the compressible gasket material of the base sheet is preserved. Thus, a gasket with enhanced sealability and compression failure resistance is provided. A unique method of making such an edge coated gasket is also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a continuation-in-part of and claims the benefit ofpriority under 35 USC §120 to all of the following copendingapplications: application Ser. No. 08/920,662, filed on Aug. 29, 1997,entitled “High-Pressure Compression Failure Resistant and High SealingGasket;” now U.S. Pat. No. 6,247,703; application Ser. No. 08/920,663,filed on Aug. 29, 1997, entitled “High Sealing Gaskets;” now U.S. Pat.No. 6,093,467; application Ser. No. 09/110,354, filed on Jul. 6, 1998,entitled “High Sealing Gaskets,” now U.S. Pat. No. 6,268,020; which is acontinuation of application Ser. No. 08/920,663 set forth above; andapplication Ser. No. 09/093,084, filed on Jun. 8, 1998, entitled “EdgeCoated Soft Gasket;” now U.S. Pat. No. 6,241,253.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to sealing devices, and moreparticularly to gaskets such as gaskets for use in gasoline and dieselengines, compressors, oil coolers, and other machinery.

2. Description of the Related Art

Gaskets have long been used to seal interfaces between components in awide variety of machines and especially in gasoline and diesel engines.For example, head gaskets seal between the heads of an engine and theengine block, oil pan gaskets seal the interface between the oil pan andthe block, and water pump gaskets seal around the ports of a water pumpwhere the water pump is attached to the engine block. Most gaskets arespecifically designed for their particular intended use. For instance,head gaskets are designed to seal against the high pressures andtemperatures and the generally caustic environment within the cylindersof an engine. On the other hand, water pump gaskets must seal againstleakage of coolant, which may consist of a water and anti-freeze mixturethat is heated and under pressure. Many if not most automotive gasketstraditionally have been made of a compressible fibrous gasket sheetmaterial that is die-cut to the required gasket shape.

In general, two key performance characteristics required of mostcompressible gaskets include compression failure resistance andsealability. Compression failure resistance refers to the ability of agasket to withstand high compression forces when clamped between twoflange surfaces without crushing, deforming, or yielding to the pointthat the mechanical properties of the gasket material and ultimately theseal provided by the gasket are compromised. Sealability refers to agasket's ability to resist or prevent leakage of fluid both between thegasket faces and the flanges between which the gasket is clamped(hereinafter referred to as interfacial leakage) and through the gasketmaterial itself (hereinafter referred to as intersticial leakage).

Leakage can be of particular concern with compressible fibrous gaskets,which generally are fabricated from sheets of material composed offiber, filler, and a binder. Because of their fibrous nature and becauseapertures of the gasket typically are die-cut, the gasket edgessurrounding the apertures tend to be somewhat porous. Since these porousedges usually are exposed to the fluid being sealed, intersticialleakage can be a particular problem with fibrous gaskets. Interfacialleakage can be caused by compression failure of the gasket material orby rough or warped flange surfaces. Thin flanges and poor bolt placementcan result in regions of substantially reduced compression stress on agasket, which also can lead to interfacial leakage.

In some instances, the sealability of a gasket can be enhanced byproviding all of the surfaces of the gasket with a coating or byimpregnating the gasket with a resin. Fibrous gaskets are particularlylikely to have such treatments since, in many cases, the porous materialof the gasket itself, although compression failure resistant, is subjectto intersticial and interfacial leakage as a result of the failuremechanisms discussed above. U.S. Pat. No. 3,661,401 discloses a gaskethaving a coating that covers both the exposed gasket faces and the edgesthat surround and define various internal apertures of the gasket. U.S.Pat. No. 4,499,135 discloses a fibrous gasket that is impregnated with asilicone resin to improve its resistance to leakage of water-antifreezemixtures. Similarly, U.S. Pat. No. 4,600,201 discloses a gasketimpregnated with a polymerizable liquid impregnating agent to enhancesealability.

While coating and impregnation can improve the sealability of a gasket,unfortunately they inherently tend to degrade the compression failureresistance of the gasket. This is because, among other things, thecoating and impregnating agents, which themselves exhibit goodsealability but poor compression failure resistance, tend to penetrateand become a part of the gasket material. This reduces the gasket'soverall compression failure resistance and thus reduces the ability ofthe gasket to function well under higher flange pressures wherecompression failure is more likely. As a result, coated and impregnatedgaskets such as those disclosed in U.S. Pat. Nos. 3,661,401, 4,499,135and 4,600,201 can perform poorly under high flange pressures, whichseverely limits the applications in which such gaskets can be used.

Other gaskets include special fillers to enhance their sealability. Forexample, U.S. Pat. No. 5,240,766 discloses a soft porous gasket sheetmaterial formed from fiber a binder, and a filler that provides enhancedsealability at higher temperatures. U.S. Pat. Nos. 5,536,565 and5,437,767 also describe a gasket sheet material formed from fiber and agel-forming mineral filler that provides the gasket with enhancedsealing properties, especially against polar liquids. While suchfillers, like coatings and impregnations, can improve the sealability ofgaskets, they also tend inherently to degrade the compression failureresistance of the gasket material and therefore reduce the ability ofthe gasket to withstand higher flange pressures. As a result, gasketswith specialized fillers to enhance sealability such as those disclosedin U.S. Pat. Nos. 5,240,766, 5,536,565 and 5,437,767 also can beseverely limited in range of application.

It will thus be appreciated that for fibrous and perhaps other types ofcompressible gaskets, sealability and compression failure resistancehave heretofore been mutually incompatible gasket properties. In otherwords, measures taken to enhance the sealability of such gasketsinherently tend to reduce compression failure resistance and vice versa.As a result, manufacturers of gaskets, and particularly fibrous gaskets,have engaged in proverbial balancing acts in order to design and producegaskets with acceptable sealability and also acceptable compressionfailure resistance for a particular application. The problem, of course,is that each of these properties necessarily becomes a compromise andneither is optimized.

Another type of gasket used in many applications is known as acontrolled compression rubber gasket. These types of gaskets incorporatemolded rubber or polymer beads that are placed into a flanged joint insuch a way that the amount of compression or compressive stress appliedto the bead is predetermined and fixed by incompressible members. Suchgaskets can take several forms. One form of a controlled compressionrubber gasket is the common O-ring gasket, wherein a molded rubber beadis nested in a groove formed in the mating surface of one of a pair offlanges. The depth and width of the groove are carefully determined suchthat the compression stress on the rubber when the flanges are boltedtogether is known and thus controlled. In another form of controlledcompression rubber gasket, a rubber bead or strip is molded onto theinterior edge of a metal or plastic shim or carrier surrounding aninterior aperture. The rubber bead is wider than the thickness of theshim and therefore can never be compressed to a thickness smaller thenthe thickness of the shim when the gasket is clamped between a pair ofmating surfaces. Thus, the amount of compression applied to the rubberbead is limited by the thickness of the shim. In another example, arubber bead is molded into grooves on one or both sides of a plasticcarrier, which is disposed in a joint to be sealed. Metallic compressionlimiters, such as washers embedded in the carrier or shouldered bolts,provide a positive compression limit on the rubber and plastic of thegasket. Controlled compression rubber gaskets may also be found in theform of a rubber sheet or coating of a specific shape and profile moldedonto both sides of a metal carrier with embedded washers or other meansof compression limitation used to control the amount of compressivestress applied to the rubber coating.

U.S. Pat. No. 5,194,696 of Read illustrates one type of controlledcompression rubber gasket wherein a rubber bead is molded onto theinterior edge of a incompressible plastic carrier, the bead being widerthan the thickness of the carrier. The gasket is placed between themating flanges of a hard disc drive case and the flanges are boltedtogether until they engage the plastic carrier. The rubber bead is thuscompressed between the flanges but never less than the thickness of thecarrier such that the compressive stress applied to the bead is limitedby the carrier thickness.

While the physical form of controlled compression gaskets varies, thesealing mechanism is common to all. Specifically, the beads of suchgaskets are formed from a polymeric or rubber compound that isreasonably stable when in contact with heat and the particular fluidbeing contained. The spring rate of the compound in conjunction with thelimited maximum compression stress provided by the carrier thickness orother compression limitation mechanism and the stiffness of the flangesyield a predetermined minimum and maximum surface stress between therubber bead and the flange surfaces sufficient to prevent interfacialleakage. Spring rate of the bead is determined by the type anddegree-of-cure of the rubber or polymer compound, the shape and contactarea of the bead, and the thickness of the bead. The thickness of thecompression limiter or depth of the groove in the case of O-ring sealsis carefully designed to yield a compression stress on the bead that issufficient to form a seal but not so high as to crush the bead. It willthus be seen that the performance of controlled compression gaskets ishighly dependent upon the characteristics of the bead material anddegree of compression provided by the compression limiting components.Too much compression can lead to crushing of the bead while too littlecan result in insufficient compression stress to establish a seal.

While controlled compression rubber gaskets have been used in manyapplications, they nevertheless suffer from a failure mechanism known asCompressive Stress Relaxation (CSR) failure in which the surface stressthat prevents interfacial leakage diminishes over time. The CSR failuremechanism is a combination of several competing effects including, butnot limited to, rearrangement of polymer molecule chains in response tothe stress state, shrinkage of the bead due to molecular chaincross-linking, softening and swelling of the bead due to fluidpenetration, and degradation of the polymer molecule chains due to heat,fluid, and oxygen exposure. Since the flange gap in which the beadresides is fixed by rigid compression limiters, these competing effectstend to reduce the compressive stress on the bead over time, which leadsto leakage. Further, controlled compression gaskets tend to besubstantially more expensive to manufacture than die-cut fibrousgaskets, which, among other factors, makes controlled compressiongaskets an unacceptable alternative to fibrous gaskets in manyapplications.

A need therefore exists for an improved compressible fibrous gasket thatretains the economy and wide application range of traditional fibrousgaskets and that also provides a superior and longer lasting seal. Theproperties of sealability and compression failure resistance should bede-coupled such that each can be optimized for a particular applicationwithout compromising the other. Such a gasket should exhibit excellentto complete sealability in a wide variety of joint types while at thesame time having the highest possible resistance to compression failurewhere such failure is likely. The failure modes associated withcontrolled compression rubber gaskets should be successfully addressed,as should problems with warped or rough flange surfaces. A method offabricating such a gasket that is economical, efficient, and reliable isalso needed. It is to the provision of such a gasket and fabricationmethod that the present invention is primarily directed.

SUMMARY OF THE INVENTION

Briefly described, the present invention, in a preferred embodimentthereof, comprises an improved compressible fibrous gasket that exhibitssimultaneously both excellent sealability in a wide range of joints andoutstanding compression failure resistance. The gasket comprises a basesheet of substantially planar contiguous fibrous gasket material havinga predetermined thickness and two opposed substantially parallel faces.The term “contiguous” as used herein means that the base sheet isuninterrupted across its flange width; that is, the gasket material ofthe base sheet extends continuously across the base sheet without breaksor innerlineations. This includes layered gaskets such as rubber coatedmetal gaskets wherein the layers are contiguous as defined herein. Ingeneral, the term “gasket material” as used herein when referring to theinvention includes any appropriate porous and/or layered material orboth, but is not intended to include rigid carriers such as the carriersof controlled compression rubber gaskets. Such carriers providemechanical support and compression limitation for their rubber seals,but generally do not contribute to the gasketing or sealing functions ofthe gasket. The term “base sheet” when used alone without beingidentified as a base sheet of gasket material is intended to includerigid carriers and all other gasket materials.

The gasket material of the invention can be any of a number oftraditional gasket sheet materials, but most preferably is a fibrousgasket material formed of a fiber and a binder and perhaps a filler. Thebase sheet has a flange width across its faces and is configured todefine at least one interior aperture bounded by a substantially porousinterior edge of the base sheet. In many instances, the aperture andinterior edge are formed by a die-cutting process, which reveals theporous internal structure of the gasket material on the interior edge. Asubstantially porous exterior edge of the gasket extends around anddefines the outside periphery of the base sheet.

An edge coating, which preferably is a polymeric coating, but that canbe formulated of a latex or other suitable material, is disposed on theporous interior edge of the base sheet surrounding the gasket aperture.The material of the edge coating at least partially penetrates theexposed pores on the edge of the base sheet forming a relatively narrowintrusion zone surrounding the aperture. This intrusion zone seals theporous edge, anchors the edge coating to the base sheet, and densitiesthe material of the base sheet in the region immediately surrounding theaperture to concentrate available compressive stress in this region whenthe gasket is clamped between mating surfaces. The coating itself isformulated and configured to engage, conform to the shape of, and adhereto the mating surfaces to establish a significantly enhanced seal ascompared to traditional fibrous gaskets.

The edge coating can take on any one of a variety of physicalconfigurations according to the particular intended use of the gasket.In one and perhaps the most preferred embodiment, the edge coating iswider than the thickness of the base sheet so that the edge coatingprojects beyond the facial planes of the base sheet to define projectingrims that extend around the aperture of the gasket. In anotherembodiment, a relatively narrow face coating is provided on one or bothfaces of base sheet extending in a strip around the aperture. The facecoatings may be formed of a different material than that of the edgecoating with the face coating abutting the edge coating around thegasket aperture. Preferably, however, the edge coating surrounding theaperture is applied in such a way that it wraps around onto the faces ofthe base sheet to form the face coatings, in which case the edge andface coatings are made of the same material. In either event, it isimportant at least in regions of high compression stress to limit thewidth and thickness of the face coating strips as detailed below tominimize their detrimental effect on the compression failure resistanceof the gasket.

A unique method of fabricating gaskets according to the presentinvention is also provided. Briefly described, the method, referred toherein as a “stack-and-coat” process, comprises stacking a predeterminednumber of cut gasket base sheets together with their apertures alignedwith each other. The aligned apertures form a cavity having the outercontours of the aperture and a depth determined by the number of gasketsin the stack. According to one preferred methodology, the base sheetsare stacked atop a plate having a shallow well formed therein, the wellhaving a shape corresponding to the shape of the gasket aperture andbeing aligned with the apertures of the stacked gaskets. Coatingmaterial, such as a polymer, in liquid form is placed in the well andthe cavity is closed off. The entire assembly is then tilted on edge androtated at a predetermined relatively slow rate and through apredetermined number of revolutions. During rotation, the liquid polymerflows around the perimeter of the cavity and contacts the exposed edgesof the stacked base sheets.

As the polymer flows around the perimeter of the cavity over and overagain, it gradually builds up on the edges of the base sheets to form acoating on the walls of the cavity with a portion of the polymerpenetrating into the porous gasket material of the edges to formintrusion zones. When a sufficient number of revolutions have beencompleted to build up a coating of a desired thickness, the assembly istilted back down to allow excess polymer to drain back into the shallowwell of the plate, whereupon the stack can be removed.

After allowing the polymer coating to thicken partially but notcompletely, the individual gaskets are peeled off of the stack.¹ Sincethe polymer is only partially thickened and thus still malleable, thepeeling of each gasket causes the polymer on the gasket's edge tostretch and deform rather like soft taffy, which results in an edgecoating that projects beyond the facial planes of the gasket to form theopposed projecting rims. The edge coatings are then fully thickened inan oven or otherwise to set the final shape and physical properties ofthe edge coating.

The terms “thicken”, “thickened”, and terms of similar import are usedherein to refer to the gradual transformation of the coating from itsmore liquid initial form to its more solid final form. “Partiallythickened” means that the coating is in a state between the two forms inwhich it retains a measure of malleability. Thickening can occur througha variety of physical and chemical mechanisms including curing (thecross-linking of polymer chains within the coating material) and drying(the evaporation of solvents from the coating material). All suchmechanisms are intended to be encompassed within the meaning of the term“thickened” as used herein.

In an alternative methodology referred to herein as a “mold-in-place”process, base sheets of gasket material are stacked with their aperturesaligned as above but with one or more spacers disposed between the basesheets. The walls of the cavity formed by the stack are coated asdescribed. The spacers have apertures that can be slightly smaller orslightly larger than the apertures of the base sheets. If a spacer witha slightly larger aperture is disposed between each base sheet, a narrowgap is formed between each sheet and polymer flows a slight distanceonto the faces of each base sheet to form overlapped face coatingssurrounding the apertures of the gaskets. Spacers with larger aperturesproduce edge coatings that do not project beyond the facial planes ofthe gasket. A precisely molded wrapped edge coating can be formed bystacking a larger aperture, then a smaller aperture, then another largeraperture spacer between each of the base sheets of gasket material. Ineither event, edge and face coatings are formed on the gaskets.

Alternative methodologies for coating the interior edges of the stackedbase sheets are also envisioned and form part of the invention. Thesealternative methodologies include a “stack-and-fill” process wherein thebase sheets are stacked and the cavity formed by their aligned aperturesis filled with a polymeric coating material. After a predetermined time,the coating material is drained or poured out of the cavity, leaving acoating on the interior edges of the gaskets. Other methodologiesinclude a “stack-and-spray” process wherein the coating material issprayed onto the interior edges of the stacked base sheets, and a“stack-and-wipe” process wherein the coating material is wiped or spreadonto the interior edges with a squeegee or other appropriate tool. Theseand other methodologies are encompassed by the stack-and-coat process ofthe present invention.

Edge coated compressible gaskets according to the present inventionprovide outstanding sealability and eliminate the failure modes oftraditional gaskets in at least the following ways. Application of apolymer edge to a compressible base sheet yields a complex sealingmechanism that maximizes tolerance to flange surface imperfections(roughness, warping, and deflection) and creates a tight fluid seal witha minimum of clamp load. This is accomplished through selection of arelatively soft conformable polymer for the edge coating that, whenapplied to form protruding rims relative to the faces of the base sheet,is highly conformable to flange surface imperfections. As the polymeredge is compressed to near the thickness of the base sheet, theattachment of the polymer edge to the base sheet provides a significantstiffening effect, which dramatically increases the spring rate of theedge in compression. This allows significant sealing force to begenerated in the polymer edge while using a soft conformable polymerthat is able to accommodate significant compression strain.

Further, the intrusion zone created by migration of the polymer into theedge pores of the base sheet creates a band of higher density around thegasket aperture, which serves to concentrate compressive load where itis most needed to enhance the seal.

Additional factors also contribute to the outstanding performance ofgaskets of this invention. These include the use of a polymer that isimpervious to the fluid to be sealed, which prevents intersticialleakage. The conforming of the edge coating to flange surfaceimperfections, the development of sealing stress through compression ofthe edge coating and the intrusion zone, and the selection of polymersthat develop surface adhesion to the flange surfaces all contribute toan outstanding seal against interfacial leakage. The combination of thesealing mechanisms of compression stress and surface adhesion results ina seal that, over time, is more tolerant to degradation of either orboth. For instance, in the event that compression stress of the polymeredge coating drops over time to a level below that needed to create aninitial seal given the flange condition, fluid type, and fluid pressure,a leak still will not occur because an adhesive bond has developedbetween the material of the edge coating and the flange surfaces.

Application of a polymer edge coating to a compressible base sheetaccording to the present invention also successfully addresses theproblem of compression stress relaxation failure common in controlledcompression rubber gaskets. Specifically, the compressible nature of thebase sheet material results in a natural thinning of the base sheet overtime due to compression stress. This thinning causes the flange surfacesto move slightly closer together over time, which actually increases thecompressive stress on the polymer edge coating. This increase incompressive stress, which cannot occur with controlled compressiongaskets, usually is more than sufficient to offset any stress relaxationthat may be experienced by the polymer edge coating.

Embodiments of the present invention with face coating strips addresscompression stress relaxation through an additional mechanism.Compression stress on the bead of a traditional controlled compressiongasket usually ranges from about 100 to 1000 pounds per square inch(psi). Compression stress relaxation can cause a loss of from 60 to near100 percent of the initial sealing stress on the bead, often resultingin insufficient compression stress to maintain a seal. However, in theface coated embodiments of the present invention, initial sealing stresson the coating material can range from 1,000 to 10,000 psi. Providedthat a polymeric material is selected that can accommodate such levelsof stress, a loss of even 90 percent of the initial sealing stress stilldoes not reduce remaining sealing stress below the level necessary tomaintain the seal. Thus, stress relaxation failure modes of traditionalprior art gaskets are virtually eliminated by edge coated gaskets of thepresent invention.

It will be appreciated from the forgoing that a unique and improvedgasket is now provided that addresses and solves the long-standingproblems with prior art gaskets. The gasket of the present invention,because of its uniquely configured high sealability edge coating,provides a seal around the aperture of the gasket that is outstandingand, in many cases, near perfect. At the same time, since the edgecoating provides such an exceptional seal, the base sheet or flangeportion of the gasket requires little or no coating or impregnation toenhance its sealability. As a result, the maximum compression failureresistance providable by the fibrous gasket material of the base sheetis preserved.

Traditional failure modes of the edge coating itself, such as stressrelaxation failure, are also virtually eliminated through the complexsealing mechanisms and edge coating configurations of the invention. Theultimate result is a highly reliable long lasting gasket that exhibitsexceptional sealability and outstanding compression failure resistancesimultaneously. In addition, the edge coating material itself can bespecifically formulated for the particular use to be made of the gasket.For example, water pump gaskets can be provided with an edge coatingthat is particularly resistant to water/anti-freeze mixtures whereas theedge coatings on oil cooler gaskets can be formulated to seal againstpetroleum based oils. Finally, the physical configuration of the edgecoating can be tailored for the particular joint type to be sealed. Forinstance, thicker wider edge coatings may be called for where the gasketis to be used with rough or warped flange surfaces or with thin flangeswhere compression stress can vary greatly due to flange deformation. Onthe other hand, thin narrow edge coatings may be chosen to seal flatsmooth flange surfaces or highly stressed joints.

While the combination of excellent sealability and preserved compressionfailure resistance is a particularly advantageous property of thepresent invention, it will be appreciated that the edge coating of theinvention provides unique advantages independent of compression failureresistance. For instance, compression failure resistance is not always aconcern or a design specification, especially when sealing joints thatare not highly stressed. In these situations, the edge coated gasket ofthis invention still provides enhanced sealability independent ofwhether or not compression failure resistance is preserved. Thus, theinvention should not be deemed to be limited to the combination of thesefeatures, although each may be present in many of the preferredembodiments disclosed herein. These and many other features, objects,and advantages of the gasket and method of the present invention willbecome more apparent upon review of the detailed description set forthbelow when taken in conjunction with the accompanying drawing figures,which are briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a gasket that embodies principles of thepresent invention in one preferred form.

FIG. 2 is a cross-sectional view of the gasket of FIG. 1 taken alongline 2—2 thereof.

FIG. 3 is a top plan view of a gasket that embodies principles of thepresent invention in an alternate preferred form.

FIG. 4 is a cross-sectional view of the gasket of FIG. 3 taken alongline 4—4 thereof.

FIGS. 5-17 are cross-sectional views illustrating various configurationsof gasket edge coatings that embody principles of the present invention.

FIG. 18 is a cross-sectional view illustrating one embodiment of thestack-and-coat manufacturing process of this invention.

FIG. 19 is a cross-section view illustrating another embodiment of thestack-and-coat process.

FIG. 20 is a cross-sectional view of yet another embodiment of thestack-and-coat process of the invention showing the formation ofprojecting rims by peeling individual gaskets from a gasket stack.

FIG. 21 is a perspective partially sectioned view of an edge coatedgasket configuration that represents a best mode of carrying out theinvention.

FIG. 22 is a perspective partially sectioned view of an edge wrappedgasket configuration that represents a best mode of carrying out theinvention.

FIG. 23 is a perspective partially sectioned view of an edge coatedgasket configuration that represents yet another best mode of carryingout the invention

FIG. 24 is a cross sectional view of an edge coated gasket having edgecoatings on both its interior and exterior edges and shown poisedbetween a pair of flange surfaces.

FIG. 25 is a cross-sectional view of another embodiment of an edgecoated gasket according to this invention showing an undercoating ofprimer disposed between the edge of the base sheet and the edge coating.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made to the attached drawing figures, wherein likereference numbers refer where appropriate to like parts throughout theseveral views. FIGS. 1 through 17 illustrate some of the wide variety ofedge coated gasket configurations encompassed by the present invention.While many of the design parameters in these illustrations are dictatedby similar application considerations and are thus the same, the variousedge coating profiles illustrated in FIGS. 1 through 17 may each beuseful in particular application specific conditions. As described inmore detail below, FIGS. 21-23 illustrate edge coated gasketconfigurations that have been found to be commercially viable and thatrepresent best mode of carrying out the invention.

FIGS. 1 and 2 illustrate a generally rectangular gasket that embodiesprinciples of the invention in one preferred form. While a simplerectangular gasket is illustrated for clarity of description in this andother figures, it will be appreciated that gaskets can and do take onany of a large number of configurations depending on the particularintended use of the gasket. Further, while a gasket with a singleaperture is illustrated in the preferred embodiments, many real worldgaskets are configured with two or more apertures and each aperture mayseal against a different type of fluid. The present invention isapplicable to any or all of the apertures of such gaskets.

The gasket 5 comprises a base sheet 10 of relatively planar gasketmaterial, which preferably is a compressible fibrous gasket material.The base sheet 10 has a flange width measured between its interior andexterior edges and is substantially contiguous, i.e. unbroken, acrossits flange width. The base sheet 10 has a thickness T and two opposedsubstantially parallel faces 8 and 9, which lie in respectivespaced-apart facial planes. Bolt holes 6 are formed in the respectivefour corners of the base sheet for accommodating bolts that attachsurrounding flanges or mating surfaces together and that are tightenedto compress the gasket 5 between the mating surfaces to create a seal.

The base sheet 10 has a fibrous internal structure and is configured,usually by a die cutting process, to define an interior aperture 7surrounded by a somewhat porous interior edge 23 of the base sheet. Anexterior edge 20 extends around the outside perimeter of the base sheet10 and usually, but not necessarily, is porous as well. The porousnature of the interior and exterior edges of the base sheet result fromthe less than fully dense gasket material and the fact that the fibrousinternal structure is exposed on the edges. Base sheets with porousinterior edges also may be formed of other gasket materials includingfoam, cork, and rubber and all such materials are encompassed within thepresent invention.

The base sheet 10 may be fabricated from any known suitable gasketmaterial that is appropriately compressible, flexible, and preferably,but not necessarily, fibrous and porous. Examples of suitable gasketmaterials include sheet gasket materials formed from a fiber and abinder or a fiber, a binder, and a filler. The present invention is alsoapplicable to composite gasket material, sometimes known as “on core”gasket material, which is formed with a first or core materialsandwiched between second or facing materials. Some specific gasketmaterial compositions suitable for use with the present invention arediscussed in greater detail below. The preferred embodiments aredescribed herein in terms of a fibrous gasket material that is flexible,compressible, and porous and that exhibits good inherent compressionfailure resistance. The invention is particularly suited for use withsuch gasket materials.

An edge coating 12 is disposed on the interior edge 23 of the base sheet10 and extends around the aperture 7. The edge coating preferably isformed of a polymer-based material that is selected or formulated to beresistant to chemical attack or degradation by the particular fluid thatis to be sealed by the gasket, to be substantially impervious to suchfluid, and to form an exceptional seal when compressed between a pair ofmetal flanges or mating surfaces. The edge coating 12 has a thicknessmeasured in a direction parallel to the facial planes of the base sheet10 and a width measured in a direction substantially transverse to thefacial planes. In FIGS. 1 and 2, the thickness of the edge coating 12 issubstantially the same across its width and the width of the edgecoating is substantially the same as the thickness T of the base sheet10. Other configurations of edge coatings are also possible andcontemplated as described in more detail below.

As illustrated at 26 in FIG. 2, the polymeric material of the edgecoating 12 intrudes a short distance into and fills the exposed poresthat characterize the interior edge 23 of the base sheet 10 forming anintrusion zone. This intersticial intrusion of the edge coating materialinto the porous edge provides a number of beneficial functions. Forexample, the intrusion anchors the edge coating 12 securely to theinterior edge 23 of the base sheet 10 so that the edge coating becomesan integral and unitary part of the gasket and will not separate fromthe edge over time, as can occur with molded rubber edge gaskets. Theintrusion of the edge coating also functions to seal off the exposedpores on the interior edge of the base sheet to inhibit intersticialseepage of fluid through the gasket. Finally, the effective density ofthe base sheet 10 is raised somewhat in the intrusion zone of theintruding polymer. It has been found that this densification tends toconcentrate available compressive stress in the region of the intrusionzone when the gasket is compressed between a pair of flange surfaces,which enhances the seal provided by the gasket. In other words, theintrusion zone enhances the ability of the gasket to create and continueto provide a seal beyond the time when compressive stress on other areasof the gasket may fall below that needed to maintain the seal.

The gasket 5 of FIGS. 1 and 2 is also provided with face coatings 11 aand coating 11 b on respective faces 8 and 9 of the base sheet 10. Facecoatings 11 a and 11 b each extend around the aperture 7 of the gasketin a relatively narrow strip having a thickness and a width. Asdiscussed in some detail above, the application of such a coating on aface or faces of the base sheet tends inherently to reduce thecompression failure resistance of the base sheet. However, by carefullyselecting the thickness and the width of the face coatings 11 a and 11b, the detrimental effects of the face coatings can be substantiallyminimized. More specifically, it has been found that the width of theface coatings 11 a and 11 b may be from about 5 mils (one mil is oneone-thousandth of an inch) to about 0.6 inches (depending on the size,configuration, and intended use of the gasket) so long as the facecoating covers less than about 50% and preferably less than about 30% ofthe facial area of the base sheet. The face coatings may not even appearin the most highly loaded areas of the gasket. It has also been foundthat the thickness of the face coatings preferably should be less thanabout 11 mils in order to minimize detrimental effects on compressionfailure resistance. Of course, these limitations are important only inregions of the gasket where compression failure resistance is required,such as in the vicinity of the bolt holes where compressive force can bevery high. In regions where compressive force is low, such as in themid-span of the bolts, compression failure resistance is not as criticala concern and face coatings with widths and thicknesses outside thepreferred ranges recited above may be used safely. Coatings 11 a and 11b are illustrated in FIGS. 1 and 2 as being formed of a differentmaterial than edge coating 12; however this should not be considered tobe a limitation of the invention.

In use, the face coatings 11 a and 11 b engage and seal against opposedflange surfaces between which the gasket is compressed. Under theseconditions, the edge coating seals against intersticial leakage of theservice fluid and the face coatings seal against interfacial leakage.The characteristics of the polymer materials from which the coatings areformed thus result in a near perfect to perfect seal around the apertureof the gasket. This seal is accomplished through a number of fundamentalmechanisms, which are discussed in some detail above. First, when thegasket is compressed between two flange surfaces, the face coatings tendto fill any imperfections such as scratches or roughness in the matingsurfaces that otherwise might result in leakage. Second, the facecoatings and to some extent the rims of the edge coating, which are theportions of the edge coating that protrude beyond the facial planes ofthe base sheet, tends to conform to any waviness or deviations fromflatness in the mating surfaces that might occur, for example, withslightly warped flanges or with thin flanges that can deflectsignificantly between bolt holes. Finally, the polymeric material of theedge coating is formulated to have a certain inherent tackiness thatcauses it to adhere to and form a bond with the flange surfaces betweenwhich the gasket is clamped. The amount of tackiness can be controlledby judicious formulation or selection of coating materials to suit aparticular application. Tackiness can also be provided if desiredthrough a layer of coating of a tacky polymer deposited on an edgecoating having otherwise desirable properties.

The edge and face coating material is selected to be impervious to andsubstantially chemically non-reactive with the particular fluid thatmust be sealed. Accordingly, these coatings essentially function as adam around the aperture 7 of the gasket to prevent both interfacial andintersticial leakage. An exceptional and in many cases a perfect seal isthus formed, even under less than perfect conditions. Further, asdiscussed in some detail above, the complex sealing mechanism formed bythe compressible base sheet and polymer edge and face coatingssuccessfully addresses stress relaxation failure and other problems withprior art controlled compression type gaskets.

FIGS. 3 and 4 illustrate an alternate embodiment of an edge coatedgasket according to the present invention. The gasket 13, which again isillustrated as a simple rectangular gasket for clarity of description,comprises a base sheet 10 having opposed substantially parallel faces 8and 9, which lie in respective facial planes. The base sheet 10preferably is formed of a substantially planar contiguous gasketmaterial that is compressible and preferably porous. While anyappropriate compressible gasket material may be used, a fibrous gasketmaterial formed of a fiber, a binder, and perhaps a filler is preferred.The base sheet 10 is die-cut or otherwise formed to define an interioraperture 7 bounded by a substantially porous interior edge 23 of thebase sheet. An exterior edge 5 extends around the perimeter of the basesheet 10 and the base sheet has a flange width as measured between itsinterior edge 23 and its exterior edge 5. Bolt holes are provided toaccommodate bolts that compress the gasket between flange surfaces toseal the joint therebetween.

An edge coating 14, which preferably is formed from a selected polymericmaterial, is disposed on the interior edge 23 of the base sheet 10. Theedge coating has a thickness in a direction parallel to the facialplanes of the base sheet 10 and a width measured in a directiontransverse to the facial planes. The width of the face coating extendsbetween respective rims 2 and 3 thereof. As seen in FIG. 4, the rims 2and 3 of the edge coating or protrude just slightly beyond respectivefacial planes of the base sheet 10. The polymeric material of the edgecoating penetrates or intrudes into the porous interior edge 23 of thebase sheet to form an intrusion zone 26, which extend around theaperture of the gasket. As in other embodiments, the intrusion zoneanchors the edge coating securely to the edge of the base sheet, sealsthe pours on the interior edge 23, and densities the gasket material inthe region of the intrusion zone.

It will be appreciated that the embodiment of FIGS. 3 and 4 has apolymer edge coating but has no portion of the faces 8 and 9 coveredwith a face coating as in the embodiment of FIGS. 1 and 2. Accordingly,while the face coatings of FIGS. 1 and 2 may cover up to about 50% oftheir respective faces, the gasket of FIGS. 3 and 4 has 0% of its facescoated with face coatings. Thus, it may be said that the face coatingsaccording to the present invention may cover from 0% to about 50% of thebase sheet 10.

Since no face coating is provided in the embodiment of FIGS. 3 and 4,the inherently high compression failure resistance of the unaffectedgasket material of the base sheet is preserved. Thus, the gasket ofFIGS. 2 and 3 functions well under conditions of higher flange pressureswhere compression failure resistance is required. At the same time, theedge coating 14 seals exceptionally well around the interior edge 23 ofthe base sheet to prevent intersticial leakage. The rims 2 and 3 of theedge coating engage, conform to, and seal against the flange surfacesbetween which the gasket is compressed. The embodiment of FIGS. 3 and 4have rims that protrude only a short distance beyond the facial planes,which is preferred for stiff smooth flanges and highly stressed joints.As discussed below, larger protruding rims of various configurations maybe preferred for sealing lower quality joints. The intrusion zone 26increases the effective material density in the region of the base sheetsurrounding the aperture. Thus, clamping load is concentrated and higheraverage flange pressures are maintained in this region. Thus, asdiscussed above relative to the embodiment of FIGS. 1 and 2, even ifcompression stress relaxation or flange warp should cause flangepressures to fall below acceptable levels in other areas of the basesheet, the flange pressure can be maintained at or above acceptablelevels in the critical region surrounding the aperture of the gasketbecause of the densified intrusion zone. The ultimate result is that agasket formed according to the embodiment of FIGS. 2 and 3 maintainssealability and substantially enhanced compression failure resistanceunder degraded flange pressure conditions.

FIGS. 5-18 illustrate a variety of alternative profiles for edgecoatings in accordance with the present invention. Each of these figuresis a cross-sectional view of a gasket and each shows an edge coatingformed on a base sheet of compressible gasket material, preferably afibrous gasket material (referenced by numeral 10 in the figures). Eachbase sheet has opposed faces 8 and 9 that lie in respective facialplanes 29 and 30. A porous interior edge 23 bounds and defines aninternal aperture of the gasket. Further, in each figure the edgecoating is shown penetrating and intruding into the porous edge 23 ofthe base sheet to form an intrusion zone 26. The edge coating in eachcase preferably is formed of a polymeric material that is selected forappropriate spring rate, tackiness, and resistance to deterioration bythe particular fluid to be sealed by the gasket. It will be appreciatedthat materials other than polymer may be used if desired.

FIG. 5 illustrates an edge coating 19 formed on the interior edge a basesheet 15. In this embodiment, no face coatings are provided and,accordingly, the gasket retains maximum compression failure resistance.The edge coating 19 has an inwardly rounded convex interior face andbeyond the facial planes 29 and 30 of the base sheet to protruding rims71 and 73 that extend around the aperture of the gasket. Edge coating isthus thicker in its central region than around its rims 71 and 73.Although many dimensions may be acceptable depending upon a particularintended application for the gasket, it has been found that the rims 71and 73 of the edge coating may protrude beyond the facial planes 29 and30 a distance of from about 1 mil to about 40 mils (one mil is oneone-thousandth of an inch) depending on the size and configuration ofthe gasket and its intended application to obtain superior sealabilityaround the aperture of the gasket.

FIG. 6 illustrates an edge coated gasket with an depressed region 51 ofthe face 8 surrounding the aperture of the gasket. The depressed region51 is configured as a relatively narrow strip surrounding the apertureand reduces the width of the interior edge of the base sheet to a widthless than the thickness of the base sheet. The depressed region 51 maybe formed intentionally through embossing techniques or may simply be anartifact of the die-cutting process. The edge coating 18 in thisembodiment is generally bulbous in shape and wraps around to cover thedepressed region 51 of the gasket face 8. A portion 71 of the edgecoating 18 protrudes beyond the facial plane 29 of the face 8 to form aprotruding rim 71 surrounding the aperture of the gasket on one sidethereof. The protruding rim 71 generally overlies the depressed region51, although this is not necessarily a requirement. The protrudingportion 71 provides extra sealability upon contact with an adjacentflange when the gasket is compressed between two flanges or other matingsurfaces. The protruding portion may extend from about 1 to about 40mils beyond the facial plane 29 depending upon the size, configuration,and intended application of the gasket.

An edge coating with the configuration shown in FIG. 6 may be formed bythe stack-and-coat methodology described briefly above and in moredetail below. In such a process, the recessed regions 51 of stackedgaskets form voids into which coating material flows. When theindividual gaskets are separated, a face coating extending over thedepressed region is formed. The final shape and size of this facecoating can be controlled to a large extent by judicial selection of thecoating rheology and the length time before the gaskets are separated. Asofter more rounded coating as shown in FIG. 6, for example, is formedwhen the coating material is softer and more malleable when individualgaskets are separated from the stack.

FIG. 7 illustrates an edge coated gasket in which the edge coating 20 isapplied only to the interior edge of a base sheet 19. The edge coating20 is seen to be generally bulbous or semi-circular in shape, and issubstantially thicker in its central portion than at its edges. In thisembodiment, the edge coating 20 has a width that is substantially thesame as the thickness of the base sheet 19 so that the rims of the edgecoating lie substantially in and do not protrude beyond the facialplanes 29 and 30. When the gasket of FIG. 7 is clamped between matingsurfaces, the edge coating seals against intersticial leakage and isslightly compressed along with the base sheet such that a relativelybroad area of the edge coating engages the flanges to seal againstinterfacial leakage. However, since there are no protruding rims in theembodiment of FIG. 7, the edge coating does not tend to conform well toflange surface imperfections and roughness. Accordingly, a gasketaccording to FIG. 7 may be preferred for use with rigid, smooth, flatflange surfaces.

FIG. 8 illustrates a gasket with a base sheet 21 that has depressedregions 75 and 76 on both faces 8 and 9 in relatively narrow stripssurrounding the aperture of the gasket. The depressed regions 75 and 76,which may be formed by embossing techniques, form a tapered strip aroundthe aperture of the gasket and result in an interior edge 23 having awidth less than the thickness of the base sheet 21. The edge coating 22is disposed on the edge 23 and also wraps around onto and substantiallycovers the depressed regions 75 and 76 of the base sheet. Further, inthe illustrated embodiment, the wrapped portions of the edge coatingprotrude slightly beyond the facial planes 29 and 30 in which the facesof the base sheet lie, although the wrapped portions might also liesubstantially in and not protrude beyond the facial planes.

When the gasket of FIG. 8 is clamped between a pair of flanges or matingsurfaces, the wrapped portions of the edge coating engage the surfacesof the flanges with a relatively large area of contact. The depressedregions 75 and 76 of the base sheet beneath the wrapped portions of theedge coating provide small cavities or recesses into which the materialof the wrapped portions can be squeezed and compressed. This tends toconcentrate the available flange load in the depressed regions. Further,the wrapped portions of the edge coating conform to rough and warpedregions of the flange surfaces to seal these imperfections. The overallresult of the large area of contact and concentrated flange pressures isan enhanced seal around the aperture of the gasket while maintaining thesuperior compression failure resistance provided by the material of thebase sheet 21.

FIG. 9 illustrates an edge coated gasket in which the edge coating isapplied only to the edge of the base sheet 24 and is configured with athickness that is substantially uniform throughout the width of thecoating. The base sheet 24 in FIG. 9 is configured as a layered gasketmaterial with a core 10 covered by layers of sheet material. A rubbercoated metal gasket is an example of such a layered configuration, andthe present invention is applicable to and includes edge coatings onlayered base sheets. The ends of the edge coating protrude beyond thefacial planes 29 and 30 of the base sheet to form a pair of protrudingrims 37 and 38 that surround the aperture of the gasket and its intendedapplication. The rims may protrude beyond the facial planes from about 1to about 40 mils depending upon the configuration and size of thegasket. When clamped between a pair of mating surfaces, the protrudingrims, 37 and 38 of the edge coating are engaged and compressed by themating surfaces before the mating surfaces engage and begin to compressthe base sheet 24 of the gasket. As a result, the rims tend to fill inand seal imperfections such as scratches or indentations that may existin the mating surfaces. Further, in situations where the mating surfacesmay be slightly warped or otherwise vary from a flat configuration, thelips 37 and 38 of the edge coating conform to the shape of the matingsurfaces, thereby accomplishing a seal against interfacial leakage offluid, even under these less than ideal conditions. The portion of theedge coating covering the edge of the gasket seals against intersticialleakage. As a result, a very good if not total seal can be achieved evenwith flange surfaces that are rough or warped or that deflect whenclamped due to the thinness of the material from which they are made.However, since there are no face coatings, compression failureresistance of the gasket is preserved. Accordingly, the edge coatedgasket of FIG. 9 may be selected for highly stressed joints that are notperfectly flat or smooth.

FIG. 10 illustrates a gasket with an edge coating that wraps around ontothe faces of the base sheet to form face coatings extending inrelatively narrow strips around the aperture of the gasket. The edgecoating 27 is slightly bulbous in its mid portion and each of thewrapped face coatings has a width measured in a direction parallel toits respective facial plane, and has a thickness. The thickness of eachface coating should be carefully selected to minimize any detrimentaleffect on the overall compression failure resistance of the gasket. Ithas been found that a thickness of the face coating in the range of fromabout 1 mil to about 11 mils forms a good seal without significantlydegrading the compression failure resistance in regions of the gasketwhere compression failure resistance is a concern. In other regions,such as in the mid-span between bolt holes, the thickness of the facecoating may range up to about 50 mils if desired. The width of the facecoatings may be from about 5 mils to about 0.6 inches depending on thesize and intended application of the gasket. In any event, each facecoating should cover no more than about 50 percent of its respectiveface and more preferably no more than about 30 percent, especially inregions of the gasket where compression failure resistance is ofgreatest concern.

The somewhat rounded contours of the edge coating in FIG. 10 may beobtained by appropriate selection of coating rheology and dwell timebefore separating individual gaskets from the stack in a stack-and-coatprocess. Use of a coating material such as latex or a 100 percent solidpolymer, which tend to relax more after separation, can also result insofter contours such as those illustrated in FIG. 10.

When the gasket of FIG. 10 is compressed between a pair of flanges, theface coatings engage and conform to the shape of the flange surfaces andadhere to the surfaces according to the tackiness of the material toform a seal against interfacial leakage. As with other embodiments, theedge coating seals the intersticial pores of the interior edge and issufficiently impervious and chemically non-reactive with the fluid beingsealed to prevent intersticial leakage. In addition, the intrusion zone26 in conjunction with the face coatings tends to concentrate availablecompression stress in a narrow strip around the aperture of the gasket.Finally, depending upon the clamping conditions, the initial compressionstress applied to the face coatings can be very large such that even ifsubstantial compression stress is lost due to stress relaxation,sufficient compression stress remains to maintain a seal. The result isan excellent to perfect seal under a wide variety of flange conditionsand compression stresses.

FIG. 11 illustrates another embodiment that is similar to the embodimentof FIG. 6 in that one of the faces of the base sheet, face 8 in theillustration, has a depressed region 42 that extends in a relativelynarrow strip around the aperture of the gasket. The depressed region 42should be less than about 0.5 inches in width. The faces 8 and 9 of thebase sheet lie in respective facial planes 29 and 30 and the interioredge 23 of the base sheet meets the interior edge of the depressedregion 42 substantially in a corner plane 82, which is intermediatefacial planes 29 and 30. The edge coating 41 is applied to the interioredge 23 of the base sheet and has a width that extends from the facialplane 30 of the base sheet to a position just beyond the corner plane82. However, in contrast to the embodiment of FIG. 6, the edge coating41 does not extend beyond or even to the facial plane 29 and thus doesnot form a face coating or a projecting rim around the aperture of thegasket. An intrusion zone 26 is formed by the intrusion of edge coatingmaterial into the porous edge 23 of the base sheet.

FIG. 12 illustrates another embodiment of an edge coated gasket thatembodies principles of the invention. This embodiment is similar in manyrespects to the embodiment of FIG. 9, except that the edge coating 48protrudes only beyond one of the facial planes, facial plane 30, to forma single protruding rim 78 around one side of the gasket's aperture. Thebase sheet 42 is provided with raised beads 46, which extend around basesheet a predetermined distance from the interior edge 23 thereof. Raisedbeads are sometimes formed in gaskets to concentrate load in the beadedregions to enhance the seal provided by the gasket. FIG. 12 is includedto illustrate that the edge coating of the present invention isapplicable to beaded as well as non-beaded gasket base sheets.Indentations 49 are also formed in and extend around the base sheet 42at a predetermined distance from the outer edge of the base sheet. Thebead 46 and indentations 49 typically are formed in the material of thebase sheet by embossing techniques, although other techniques may alsobe used.

FIG. 13 illustrates yet another embodiment of the invention wherein agasket base sheet 44 is provided with a uniquely configured edge coating112. As in the embodiment of FIG. 10, the edge coating 112 in FIG. 13wraps around onto the faces 8 and 9 of the base sheet to form facecoatings 111 that extend in relatively narrow strips around the apertureof the gasket. The face coatings 111 have a thickness in regions wherecompression failure resistance is required that preferably is less thanabout 11 mils and a width that covers less than 50 percent andpreferably less than 30 percent of the faces of the base sheet 44.Unlike the embodiment of FIG. 10, however, the edge coating 112 in thisembodiment protrudes beyond the facial planes 29 and 30 and alsoprotrudes beyond the face coatings 111 to form protruding rims 71 and 81around the aperture of the gasket. Preferably, the rims 76 and 81protrude beyond the face coatings 111 a distance of from about 1 toabout 40 mils, although other degrees of protrusion may be selecteddepending on the size and intended application of the gasket.

As the gasket of FIG. 13 is compressed between a pair flanges, thesurfaces of the flanges first engage the rims 71 and 81 of the edgecoating, which fill imperfections in the surfaces. Further, because oftheir exaggerated extension beyond the facial planes, the rims 76 and 81conform well to any warping, deflection, or other deviations fromflatness in the surfaces of the flanges. A good to perfect seal can thusbe formed even when the surfaces of the flanges are in less than idealcondition. As the flanges are tightened further, their surfaces engagethe face coatings 111 to enhance the seal and eventually engage andcompress the gasket material of the base sheet 44. The result is anexceptional seal around the aperture of the gasket provided by the edgeand face coatings as well as outstanding compression failure resistanceprovided by the fibrous gasket material of the base sheet 44. Even ifthe flange pressure on the base sheet or on any portion thereof fallsbelow an acceptable level because, for example, of flange surfacewarping or poorly designed bolt placement, a good seal against bothintersticial and interfacial leakage is maintained by the edge and facecoatings of the gasket. Further, the very high initial flange pressureson the face coatings provides exceptional stress relaxation failureresistance, as detailed above.

FIG. 14 illustrates yet another configuration of a possible edge coatingon a compressible fibrous gasket that embodies principles of theinvention. In this embodiment, the edge coating 85 is disposed on andpenetrates the pores of the interior edge 23 of the base sheet as inother embodiments. The edge coating protrudes in this embodiment adistance D1 beyond the facial planes 29 and 30 to form protruding rims120 and 122. In the illustrated embodiment, the edge coating 85protrudes beyond both facial planes the same distance D1. However, itwill be appreciated that these protruding distances may also bedifferent from each other depending upon the intended application of thegasket.

The edge coating 85 has an interior surface that is substantially convexbetween the rims 120 and 122 such that the edge coating is substantiallythicker in its mid-portion than at its ends. The maximum thickness ofthe edge coating from the edge 23 of the base sheet to the interiorsurface of the edge coating is D2. It has been found that for a standard{fraction (1/32)} (0.031) inch thick automotive gasket, a distance D1 ofbetween 1 and 40 mils in conjunction with a distance D2 of between 1 and50 mils can be used depending on the size of the gasket and its intendedapplication. More generally, it has been found that a ratio of distanceD1 to distance D2 of between about 0.1 and 3 is preferred. The optimumvalues of D1 and D2 can vary greatly depending upon the conditions underwhich a seal must be established. These values for a particularcircumstance are dictated by a number of application specific factorssuch as the stiffness of the mating surfaces, their roughness, theirflatness, whether or not the mating surfaces are machined, and whetheror not the mating surfaces are likely to be mismatched. In general,however, the more precise, flat, and smooth the mating surfaces and thethicker the mating flanges, the smaller D1 is required to be to obtain atargeted sealability. On the other hand, when a seal must be establishedbetween mating surfaces that are imprecise, warped, rough, or wheremating flanges are thin and tend to deflect, a larger value of D1 may berequired to fill voids and establish the desired seal. One importantadvantage of the present invention is precisely that it is so adaptableto a wide variety of flange types and conditions simply by tailoring theedge coating to match the conditions under which sealability must beestablished.

FIG. 15 illustrates another embodiment of the invention that is slightlydifferent from the embodiment of FIG. 14. Here the edge coating issimilar in shape to that of FIG. 14 having a convex interior surface andprotruding beyond facial planes 29 and 30 a distance D1. The maximumthickness of the edge coating 89 is D2. As with the prior embodiment,the distance D1 preferably is between about 1 and 40 mils and thedistance D2 preferably is between about 1 and 50 mils, however, otherdistances may be chosen depending upon the conditions under which thegasket is to be used. In any event, a ratio of the distance D1 to thedistance D2 of between about 0.1 and 3 is preferable in most standardautomotive applications.

The edge coating 89 in FIG. 15 extends or wraps a relatively shortdistance onto the respective faces 8 and 9 of the base sheet 52 to formface coatings 86 and 88, which extend in strips around the aperture ofthe gasket. The thickness and width of the face coatings 86 and 88 areselected to minimize any adverse impact on the compression failureresistance provided by the base sheet, at least in regions of the gasketwhere compression failure is a possibility. A thickness of the facecoatings in such regions of less than about 11 mils and a width selectedto cover less than about 50 percent of the faces of the base sheet ispreferable, but not necessarily a requirement.

FIG. 16 illustrates another embodiment of an edge coated gasket thatembodies principles of the invention. Here, the edge coating 90 isbonded to and penetrates the interior edge 23 of the base sheet 56 toform intrusion zone 26 and significantly overlaps onto the respectivefaces 8 and 9 thereof. The edge coating 90 has a substantially roundedinterior face that extends between rather sharp or pointed extreme ends140 and 142 of the protruding rims. The edge coating 90 has a maximumthickness T measured from the interior edge 23 of the base sheet andprotrudes beyond the facial planes 29 and 30 a distance D3. The degreeof protrusion beyond each of the facial planes in FIG. 16 issubstantially the same. However, this is not a requirement of theinvention and the distances could indeed be different depending on theintended application of the gasket.

The edge coating wraps onto the respective faces 8 and 9 of the basesheet a distance D4. It has been found preferable for a standard 0.031inch thick automotive gasket that the maximum thickness T of the edgecoating be about 50 mils and that the distance D3 that the edge coatingprotrudes beyond the facial planes be less than about 40 mils. It shouldbe understood, however, that these distances may well be different fromthe preferred values depending upon the size and configuration of thegasket and its intended application. In any event, it has been foundthat a ratio of protrusion distance D3 to the thickness T of the edgecoating preferably is in the range of from about 0.1 to about 3 toobtain superior sealability under most conditions.

The distance D4 that the edge coating wraps onto the faces 8 and 9 ofthe base sheet should be sufficiently small to minimize detrimentaleffects on the compression failure resistance of the gasket material (atleast in regions where such is a concern) and sufficiently large toprovide additional structural support, conformability, and rigidity tothe edge coating. It has been found that a distance D4 of from about 5mils to about 0.6 inches functions well in most applications, althoughdifferent overlapping distances may be chosen. In any event, thedistance D4 should be selected such that no more that about 50 percentand preferably no more than about 30 percent of the gasket faces arecovered, at least in regions where good compression failure resistanceis required. The protruding rims of the edge coating may be formed byseparating stacked edge coated gaskets before the edge coating materialis completely thickened in a “stack and coat” fabrication processdescribed in more detail below. The relatively sharp nature of the rimsresults from a thicker less malleable rheology of the coating materialat the time of separation.

In FIG. 16, the relative sharp extreme ends 140 and 142 are alignedslightly behind the interior edge of the base sheet. The final positionof these extreme ends, which are artifacts of the separation processduring fabrication, relative to the interior edge can be controlled byselecting the width D4 of the face coatings. For example, if the widthof the face coating is less than that shown in FIG. 16, the extreme ends140 and 142 will move to the right. For face coating widths less thansome threshold, the extreme ends will align inside the interior edge andwithin the aperture of the gasket. Such a configuration may be preferredin many situations such as, for example, when sealing between warpedflanges. In any event, the position of the sharp extreme ends relativeto the interior edge can be predetermined to meet application specificrequirements.

FIG. 17 illustrates another embodiment of the invention. Here, the edgecoating 91 is applied to the interior edge 23 of the base sheet 58 andhas a thickness T and a relatively flat inner face that is not bulbousor curved in cross-section. The edge coating protrudes beyond the facialplanes 29 and 30 a distance D5 to form rims and the protruding rims areinwardly tapered beyond the facial planes to relatively narrow extremeends 144 and 146. As with other embodiments, the protruding distance D5in FIG. 17 for most standard automotive gaskets preferably is betweenabout 1 mil and about 40 mils. The thickness T of the edge coatingpreferably between about 1 mil and about 50 mils. However, distancesother than these may be selected for a particular gasket andapplication. In any event, the ratio of the protruding distance D5 tothe thickness T preferably is between about 0.1 and 3.

As mentioned above, it has been found that compression failureresistance can be retained, at least in regions of the gasket wherecompression failure is possible, by limiting the thickness and width ofthe coatings on the faces of the base sheet. For the embodimentsdisclosed in FIGS. 2, 6, 8, 10, 13 and 15, the face coatings may have awidth of up to about 0.6 inches from the interior edge of the basesheet, as long as the coating does not cover more than about 50 percentand most preferably no more than about 30 percent of the facialsurfaces.

The thickness of the face coatings on the interior edge of the basesheet for each of these embodiments may vary significantly dependingupon the size and configuration of the gasket and its intended end use.Generally, the greater the thickness of the edge coating, the lower theflange pressure at which compression failure of the gasket can occur.Since in most cases, the edge coating is intended to seal both againstintersticial leakage and interfacial leakage, any coating thickness andconfiguration sufficient to provide such a seal is within the scope ofthe invention.

Since the fluid to be sealed generally contacts the gasket first at theinterior edge bounding the aperture, coatings on the interior edge forma primary seal. When such a seal is established properly, fluid isprevented from reaching and coming into contact with the gasket materialof the base sheet itself. Thus, prior problems associated with gradualdegradation of the seal and resulting leakage due to progressivedeterioration of the gasket material by the fluid is prevented. In thepast, such degradation has not been uncommon and can be particularlyserious where a single gasket must be designed to seal against differenttypes of conditions. For example, the head gasket of an engine must sealagainst the high pressures and temperatures and the corrosiveenvironment within the cylinders of the engine while at the same timesealing against leakage of coolant circulating through the engine'swater jacket. If the gasket deteriorates due to exposure to either ofthese conditions, the segregation between the cylinders and water jacketcan be lost and coolant can leak into the engine's cylinders and intothe oil, which quickly can ruin the entire engine. The present inventionprevents such failures by eliminating direct contact between the fluidbeing sealed and the gasket material from which the gaskets are made.Further, a different fluid specific edge coating material can beselected for each internal aperture of the gasket to customize eachaperture for sealing against a particular fluid or environment.

In the illustrated embodiments discussed above, edge and facial coatingshave been illustrated only around the interior aperture or apertures ofa gasket. Such interior edge coatings provide exceptional sealabilityunder many common conditions here pressurized or unpressurized fluidsare being sealed in. For example, internally edge coated water pumpgaskets provide exceptional seals against leakage of pressurized heatedcoolant from within an engine. Oil pan and oil cooler gaskets withinterior edge coatings seal well against leakage of heated oil that mayor may not be under pressure. In some instances, however, it is desiredto seal not against the escape of a contained fluid but rather againstthe leakage of ambient atmosphere into a sealed area. One example is thesealing of the cylinder or cylinders of a vacuum pump, whereinsubstantial vacuums are created as the piston of the pump reciprocateswithin the cylinder. An engine's intake manifold gasket is anotherexample of a gasket that seals against leakage into rather than out ofthe sealed area. In these and other situations, the invention may beimplemented as detailed below relative to FIG. 24 by applying an edgecoating to the exterior outside edge of a gasket instead of or inaddition to an interior edge coating. The exterior edge coating thenbecomes the primary seal against intersticial and interfacial leakage ofambient atmosphere into the cylinder and functions just as the interioredge coatings described hereinabove, but in the opposite direction.Gaskets with interior and exterior edge coatings, or both, are intendedto be within the scope of the present invention.

Suitable materials for use as the edge and face coatings of thisinvention vary widely depending upon the flange conditions and servicefluids to be sealed. Generally, however, such materials include fusiblepowders, solid-filled polymers, and 100% solid fluids. Latex and/orelastomeric materials as well as silicone based materials and arepreferred under some conditions. Specific preferred materials include,but are not limited to, organic, inorganic, and inorganic/organic hybridpolymers as well as filled polymers. Other polymeric coatings mayinclude, but are not limited to, materials such as acrylic,acrylonitrile, acrylonitrile butadiene rubber NBR, fluoro polymers,hydrogenated NBR, styrene butadiene polymer, fluoroelastomer polymer,acrylic-acrylonitrile polymers, carboxylated acrylonitrile polymer,carboxylated styrene butadiene polymer, polyvinylidene chloride,chloroprene rubber polymer, ethylene propylene rubber polymer,ethylene/vinyl acetate polymer, epoxy, fluorosilicones, polyurethane,and silicone rubber. Each of the above materials may be UV curable, heatcurable, or room temperature curable, or may require combinations ofcuring techniques. A polymeric coating may include a variety of fillerssuch as, for example, silica, carbon black, or clay to provide materialproperties adapted to a particular fluid or condition to be sealed.Polymeric powders that are heat fusible onto the faces and/or edges ofthe gasket base sheet also are acceptable and may be preferable forcertain types of gaskets. Different, more exotic, or custom formulatedmaterials now known or yet to be developed may be substituted for thesepreferred coating materials within the scope of this invention. Thus,while preferred materials are disclosed, the invention is not and shouldnot be considered to be limited to the disclosed materials. Any materialcapable of providing the disclosed sealing properties is intended to beincluded within the scope of the invention.

Materials from which the base sheets of gaskets of the invention alsomay vary depending upon the intended application of the gasket. However,the base sheet preferably should be made of a compressible gasketmaterial to take advantage of the complex sealing mechanisms discussedherein. Acceptable materials include, but are not limited to, fibrousgasket sheet materials, uncoated gasket materials, gasket materials withrelease coatings, soft gasket materials, and layered or laminated gasketmaterials sometimes called on-core gasket materials. An example of anon-core gasket material is a composite sheet with a compressible ornon-compressible core having one desired property sandwiched between twolayers of a second gasket material having another desired property.Engine head gaskets generally are made from on-core gasket materials.Where the base sheet is made from an on-core gasket material, an edgecoating may be applied to less than all of the layers of the laminatesuch as, for example, only layers with porous edges, to seal againstintersticial leakage. Preferably, however, the edge coating is formed onall of the layers to provide a continuous seal across the width of thegasket and to seal against leakage that may occur between layers of thegasket.

As mentioned above, the present invention has been found to beparticularly advantageous when compressible fibrous gasket sheetmaterial is used as the base sheet of the gasket. Examples of suchmaterials that are commercially available include gasket sheet materialsmarketed under the trade names Synthaseal™, Pro-Formance™, andMicropore™. Most fibrous gasket materials are made principally from afiber, a binder, and in some cases a filler, each included inproportional amounts. Although a wide range of proportional amounts arepossible, gasket materials having at least 1% by weight of a binder andat least 5% by weight of a fiber have been found to be acceptable.Fillers can be added at a minimum level of about 1% by weight. Suitableranges for these components include a range of from about 3% to about40% by weight binder, from about 5% to about 70% by weight of a fiber,and, where applicable, from about 1% to about 92% by weight filler.

Types of gaskets particularly suitable for application of the presentinvention include, but certainly are not limited to, intake manifoldgaskets for internal combustion engines, oil pan gaskets, valve covergaskets, fuel pump gaskets, differential cover gaskets, transmissioncover gaskets, water pump gaskets, air conditioning compressor gaskets,gas meter gaskets, and a variety of coupling flange gaskets forindustrial pipelines, steam conduits, and other plumbing connections.The fluid to be sealed in each case will dictate to some extent thematerial selected to form the edge coatings of the gasket because theedge coating generally is in constant contact and must be chemicallycompatible with the fluid. For example, Chloroprene polymer oracrylonitrile may be preferred edge coating materials for gasketsexposed to refrigerants whereas acrylic or acrylonitrile may bepreferred where oil is the fluid to be sealed.

The preferred embodiments have been described as having edge coatingscovering all of the interior edge of the gasket's base sheet, which ispreferred. However, it is also contemplated that less than all of theedge may be coated in some circumstances to conserve material and reducecosts without substantially degrading the sealability provided by theedge coating. For example, portions of the interior edge that are in thevicinity of bolt holes may not require an edge coating because theadditional flange pressure applied in these regions reduce the need toprovide an ancillary seal. However, superior sealability still isobtained by coating the entire interior edge. Accordingly, while partialedge coatings are intended to be within the scope of the invention,complete edge coatings are preferred.

Release coatings are sometimes applied to gaskets and particularly tofibrous gaskets to reduce gasket adhesion to mating surfaces and to makea spent gasket easier to remove after use. Release coatings typicallyare very thin, usually substantially less than 1 mil, and are designedto be surface coatings that do not penetrate the material of the gasketbase sheet. Accordingly, most, but not all release coatings do notdetrimentally affect the compression failure resistance of the gasketmaterial. One example of a commonly used release coating that does notaffect compression failure resistance of the gasket base sheet isformulated as a mica or vermiculite dispersion. The present inventionencompasses and is applicable to gasket base sheet materials with andwithout release coatings.

Embodiments of the invention with edge coatings only and not facecoatings have been found to be suitable for applications where higherflange pressures up to about 30,000 PSI are to be encountered by thegasket. Embodiments that include face coatings on one or both faces inaddition to an edge coating have been found to be suitable for use withlower flange pressures up to about 15,000 PSI.

FIGS. 18 through 20 illustrate a unique methodology for fabricating edgecoated gaskets of the present invention. The method generally isreferred to herein as a “stack-and-coat” process and will be describedin terms of specific embodiments and methodologies, although theinvention is not limited to the particular exemplary embodiments.Generally, the stack-and-coat process of this invention comprisesstacking a plurality of gasket base sheets together in a stack with thebase sheets being aligned with each other. When stacked, the interioredges of the gaskets, each of which defines its gasket's aperture, alignwith each other to form a cavity. The cavity has a peripheral contourcorresponding to the shape of the individual apertures and a depthdetermined by the number of gaskets stacked together. The interior edgesof the gaskets are exposed on and define the walls of the cavity.

In one preferred methodology referred to as a “stack-and-rotate”process, the gaskets are stacked atop a base, which may be made ofPlexiglas or other machinable material. The base is pre-machined todefine a relatively shallow well having the size and contour of theapertures of the gaskets and the gaskets are positioned on the base sothat the well is aligned with the cavity formed by the stack. The basethus closes off one end of the cavity and the floor of the shallow welldefines the bottom of the cavity formed by the stacked gaskets. The wellis filled or at least partially filled with an edge coating material,such as a polymeric material, in liquid form. The cavity is then closedoff at its top end by, for example, clamping the entire gasket stack andbase securely between a pair of heavy metal plates, which compress thegasket base sheets together tightly and seals off the open end of thecavity formed thereby.

With liquid polymer in the well and the cavity sealed between the metalplates, the entire assembly is tilted up on edge at a predetermined rateof tilt. This causes the liquid polymer to flow out of the well and ontothe edges of the gasket base sheets. The rate of tilt is selected toinsure even flow of polymer onto the edges and to prevent splashing oragitation of the polymer that might entrain air bubbles. While theoptimum tilt rate for a particular situation is highly dependent uponfactors such as the coating rheology, its viscosity, the base sheetmaterial, and the complexity of the aperture shape, it has been foundgenerally that tilt rates of less than about 3 to 4 degrees per secondare acceptable for most applications.

When the stack has been tilted onto its edge, it is rotated about theaxis of the cavity at a predetermined relatively slow rotation rate andthrough a predetermined number of rotations. During each completerotation, the liquid polymer or other coating material flows under theinfluence of gravity completely around the interior wall of the cavity.In this way, the polymer is progressively deposited and builds up on theinterior edges of the stacked gaskets to form their respective intrusionzones. The rate of rotation of the stacked gaskets is selected to insurethat the coating material flows evenly around the cavity, that it flowscompletely into any crevices formed by the profile of the apertures, andthat the coating material penetrates the porous interior edges of thestacked gaskets. Again, while the optimum rotation rate is dictated bymany factors, it has been found generally that rotation rates from about0.5 rotations per minute (rpm) to about 30 rpm are acceptable in mostsituations.

When the coating material has built up on the walls of the cavity to apredetermined thickness, rotation is discontinued and the assembly istilted back down to allow excess coating material to flow back into theshallow well formed in the base. After excess coating material hasdrained away, a stack of gasket base sheets with a continuous coatingcovering the walls of the cavity formed by the exposed interior edges ofthe gaskets is formed.

Other methodologies of coating the walls of the cavity formed by a stackof gaskets have been used and each can be as acceptable as thestack-and-rotate methodology described above. These alternativemethodologies will not be described in detail, but, in general, theyinclude a “stack-and-fill” process, a “stack-and-spray” process, a“stack-and-wipe” process and a “stack-and-flame spray” process. In the“stack-and-fill” process, the cavity (or cavities) formed by a stack ofgaskets is filled with the coating material in liquid form, which isleft to set for a predetermined time. The coating material is thenpoured out of the cavity, leaving behind a continuous coating coveringwalls of the cavity formed by the exposed interior edges of the stackedgaskets. In the stack-and-spray process, the coating material is sprayedonto the walls of the cavity formed by the aligned interior edges of astack of gaskets, again resulting in a continuous coating on the exposedinterior edges of the gaskets. In the stack-and-wipe process, thecoating material is applied to the exposed edges of a stack of gasketsusing an appropriate tool such as a squeegee. Finally, in thestack-and-flame spray process, the coating material is caused tocoagulate onto the exposed edges of the gaskets through a flame sprayingprocess. The result of each of these methodologies is the same; acontinuous coating on the aligned interior edges of the stacked basesheets.

With a continuous coating covering the interior edges of the stackedbase sheets, the stack is removed from the coating apparatus and theedge coating material, which now coats the walls of the cavity formed bythe stack, is allow to thicken partially but not completely such that itretains a degree of malleability. With the coating material partiallythickened and malleable, each individual gasket is peeled off of thestack of gaskets. The peeling process causes the coating material on theedge of each gasket to be torn from the continuous coating on the wallsof the cavity formed by the remaining gaskets. An edge coating on eachgasket that is torn away is thus formed. Further, and significantly,since the edge coating material in most applications is only partiallythickened and still malleable, the tearing away process stretches theedge coating material and elongates it to form the raised rims of theedge coating that protrude beyond the facial planes of the torn awaygasket. By selecting coating material rheology, material build up, andpartial thickening or dwell times in conjunction with the use of varioustypes of spacers in the gasket stack, a wide variety of edge coatingconfigurations, many of which are illustrated in FIGS. 5 through 17, canbe formed.

When the individual edge coated gaskets have been peeled from the stack,the thickening of the edge coating material is completed to set theshape and final properties of the edge coating. In the case of polymericedge coatings, the final thickening may be accomplished by moving thegaskets through a curing oven to accelerate the curing, i.e. thecross-linking, of the polymer. For other types of coating materialswhere drying is the mechanism by which thickening occurs, ovens may alsobe used to accelerate the evaporation of solvents from the coatingmaterial to complete the thickening thereof.

With their edge coatings fully thickened, the finished edge coatedgaskets may be individually tested and certified as providing anacceptable seal, whereupon they are packaged for shipment to the enduser. One method of testing and certifying the gaskets is to place eachgasket between a pair of metal plates. The plates are then movedtogether toward the gasket until the edge coating is contacted and atleast partially compressed by the plates. The final spacing between theplates and thus the compression stress applied to the edge coatings canbe determined by metal spacers and is selected to prevent permanentdistortion or deformation of the edge coatings while at the same timeapplying sufficient compression stress to create a seal. Compressed airis then pumped into the aperture of the gasket to a predeterminedpressure and the pressure remaining after a set time period is noted. Ifthe pressure does not change or if it changes less than a predeterminedthreshold amount, then the gasket is certified as providing the desiredseal. The test also can be performed by drawing a predetermined vacuumin the aperture of the gasket and measuring the decay in the vacuum overtime or after a predetermined time.

FIG. 20 illustrates the peeling process discussed above for creatingedge coated gaskets with projecting rims that protrude beyond the facialplanes of the gasket. Here a plurality of gasket base sheets 201 areseen to be stacked together with their interior edges aligned to definethe walls of the cavity. In this figure, the stack has previouslyundergone one of the coating processes discussed above such that acontinuous barrier 216 of edge coating material covers the exposed edgesof the stacked gaskets to a predetermined depth. Further, the materialof the barrier 216, which may be a polymeric material, is partially butnot completely thickened such that it retains a measure of malleability.The top gasket of the stack is shown being peeled off of the stack inthe general direction of arrows 215 to separate it from the remaininggaskets in the stack.

As the top gasket is peeled away, the edge coating material on its edgeis progressively torn from the continuous barrier 216, forming edgecoating 217 extending around the aperture of the torn-away gasket. Sincethe edge coating material is still malleable, the tearing processstretches and deforms the coating material along the line of the tear toform a rim 218 that protrudes beyond the facial plane of the base sheet.The other torn edge left on the stack is also stretched during thetearing process as indicated at 219. The result for each gasket peeledaway is an edge coating having a pair of opposed projecting rims 218 and219 that extend around the aperture of the gasket. Thickening of theindividual edge coatings is then accomplished by curing or drying asdiscussed above to set the shape and elastic properties of the edgecoatings. Edge coating configurations such as those illustrated in FIGS.5, 14, 15, and 17 may be made using the embodiment of the processillustrated in FIG. 20

FIG. 18 illustrates another embodiment of the stack and coat processreferred to herein as the “mold-in-place” process. In this embodiment,gasket base sheets 201 are again stacked with their interior edges 204aligned with each other. However, in this embodiment, spacers 206 aredisposed between each pair of base sheets 201 in the stack. The spacers206, which preferably are made of a non-stick material such as nylon orTeflon, are formed with apertures that have the same shape as theapertures of the base sheets but that are slightly larger. The interioredges of the spacers 206 are thus recessed with respect to the alignededges of the base sheets. FIG. 18 illustrates the spaced stack as itappears after having been coated with edge coating material 207 such as,for example, a polymer coating. The edge coating material 207 covers andpenetrates the interior edges 204 of the base sheets to form theirintrusion zones and also extends into the recessed space created by aspacer between each of the base sheets. It will thus be seen that theedge coating material wraps around partially onto the faces 202 and 203of each base sheet to form face coatings that extend in strips aroundthe apertures of the gaskets.

Just as in the embodiment of FIG. 20, the gaskets 201 in themold-in-place process of FIG. 18 may be peeled away from the stack at atime when the edge coating material is partially thickened and stillmalleable. This causes the edge coating material to tear and to stretchand deform in the regions of the recesses between the gaskets to formedge and face coated gaskets with projecting rims that protrude beyondthe facial planes of the gaskets. The thickening is then completed in acuring oven or otherwise to set the final shape and properties of theedge coatings. Gaskets with edge coating configurations such as thoseshown in FIGS. 13, and 16 may be formed by the mold-in-place processillustrated in FIG. 18.

FIG. 19 illustrates yet another mold-in-place process for manufacturingedge coated gaskets that exhibit features of the invention. In thisembodiment, gasket base sheets 201 are stacked with their interior edges204 aligned with each other. A set of stacked spacers 208, 209, and 211are disposed between each pair of base sheets. Spacers 208 and 211 aredisposed against the base sheets and have apertures that are slightlylarger than the apertures of the base sheets to define recesses 221 and222. Spacer 209 is sandwiched between spacers 208 and 211 and is formedwith an aperture that is slightly smaller than the apertures of the basesheets such that spacers 209 extend to an edge that projects beyond thealigned interior edges 204 of the base sheets.

The stacked assembly in FIG. 19 is shown as it appears after theapplication of edge coating material through one of the processesdescribed above or otherwise. It can be seen that edge coating materialhas flowed onto the interior edges 204 of each of the gasket base sheetsand has penetrated the pores thereof to form intrusion zones. Edgecoating material also has flowed into the recesses 221 and 222 formed bythe spacers 208, 209, and 211 to form wrapped face coatings that extendin strips around the apertures of the gaskets. Because of the extensionof the middle spacers 209 beyond the edges of the base sheets, the facecoating strips take on a well defined molded shape. When the gaskets arepulled from the stack, the stretching and deformation of the edgecoating material discussed relative to FIGS. 18 and 20 does not occurbecause the material on each edge is separated by the material onadjacent gaskets by the spacer 223. In this regard, the coating materialmay be allowed to thicken fully before the individual gaskets are peeledfrom the stack if desired since elongation of the coating material todefine raised rims is not required. The result is a molded wrapped edgeand face coating that can be precisely dimensioned and shaped byselection of spacers having appropriate thicknesses and aperture sizes.For example, if thinner face coatings are desired, then spacers 208 and211 can be relatively thinner whereas relatively thicker spacers resultin relatively thicker face coatings. The embodiment of the process shownif FIG. 19 is useful for producing edge coated gaskets with cleanlymolded edges such as those illustrated in FIGS. 4, 7, 8, 9, and 13.

While three embodiments of the mold-in-place manufacturing process ofthe invention have been illustrated, it will be understood that numerousvariations of the illustrated and described embodiments are possible.For example, a variety of thicknesses of spacers with a variety of sizesand shapes of apertures may be used to form edge coatings with an equalvariety of shapes and advantages. Thus, the exemplary embodimentsdescribed herein should not be considered exhaustive but are providedonly as examples of the preferred mode of practicing the invention.

While FIGS. 1 through 17 illustrate many possible configurations of edgecoatings that embody principles of the invention, FIGS. 21 through 23illustrate three preferred configurations that have proven advantageousand that together represent the best mode known to the inventors ofcarrying out the invention. FIG. 21 illustrates an edge coated gasket251 comprising a base sheet 252 of a compressible fibrous gasketmaterial. The base sheet 252 has opposed faces 253 and 254 that lie inrespective facial planes and that bound a substantially porous internalstructure 256 of the base sheet. As detailed above, the gasket materialof the base sheet may be any of a wide variety of gasket materialsdepending upon the conditions of the intended use of the gasket. Thebase sheet 252 is die-cut or otherwise formed to have an interior edge257 that surrounds an aperture of the gasket.

An edge coating 258 is disposed on the interior edge 257 of the basesheet and preferably, but not necessarily, is formed of a polymericmaterial appropriate for the particular fluid type and physicalconditions to which the gasket will be exposed. The edge coating has acentral portion 259, a first projecting rim 261 that projects beyond thefacial plane in which face 253 lies, and a second projecting rim 262that projects beyond the facial plane in which face 254 lies.

The edge coating 258 is formed by the stack-and-coat process outlinedabove relative to FIG. 20. During the process, the dwell time beforeindividual gaskets are peeled from the stack is chosen in conjunctionwith the rheology of the polymeric material to produce an edge coatingwith the configuration and generally soft rounded contours illustratedin FIG. 21. More specifically, the edge coating 258 is relativelythicker in its central portion 259 and gradually decreases in thicknesstoward the protruding rims 261 and 262. The extreme edges of the rims261 and 262 are also somewhat smoothly contoured as shown.

The polymeric material of the edge coating 258 penetrates the porousinterior edge 257 of the base sheet a predetermined distance to form anintrusion zone 263 within which the pores of the gasket material aresubstantially filled and closed by the polymeric material. As detailedabove, the intrusion of the polymeric material functions to seal off theporous interior edge of the base sheet, bond the edge coating firmly tothe edge, and to form a strip of relatively higher overall densitysurrounding the aperture of the gasket to concentrate compression loadin this region. If the base sheet 252 is made of a standard automotivegasket material with a thickness of 0.031 inches, then the rims 261 and262 preferably protrude beyond the facial planes a distance of betweenabout 1 to about 40 mils and the thickness of the edge coating in itscentral region preferably is between about 1 and about 50 mills, alldepending upon the intended application of the gasket. The preferredratio of the protruding distance to the thickness for most situations isbetween about 0.1 and about 3.

The edge coated gasket of FIG. 21 has been found to provide outstandingperformance in a wide variety of sealing environments. The geometry ofthe coating exhibits a relatively low spring rate at the tips of theprotruding rims, which allows the edge coating to conform to andaccommodate rough and/or irregularly shaped flange surfaces. When theedge coating is compressed between flange surfaces, the coating-edgeinterface and the intrusion zone add stiffness and generate considerablesealing force under full compression.

Stress relaxation, which is a common failure mode in controlledcompression rubber gaskets, is addressed by the gasket of FIG. 21 in atleast two ways. First, the base sheet is compressible rather than rigid.This actually improves the polymer edge compression over time as thebase sheet gradually compresses under the load of the joint. Second, thesealing mechanism of the polymer edge coating is a combination ofsealing stress and surface adhesion to the flange surfaces. Therefore,even if sealing stress on the edge coating decreases over time, the sealprovided by the coating is not likely to be compromised. The result is aseal of exceptional integrity and longevity far beyond that provided bya gasket without an edge coating or even a controlled compression rubbergasket. Further, shear stresses in a joint are accommodated by theelasticity of the edge coating and the compressible base sheet material,which can extend up to 20 percent of its thickness under shear loadswithout sliding on the flange surfaces. Surface abrasion andrubber-to-carrier delamination, which often causes failure of controlledcompression rubber gaskets, is thus virtually eliminated.

FIG. 22 illustrates the best mode known to the inventors of carrying outthe wrapped edge embodiment of the present invention. The edge coatingconfiguration shown here results from the mold-in-place fabricationprocess described above relative to FIG. 19. Edge coated gasket 266comprises a compressible porous base sheet 267 of gasket material havingfaces 268 and 269 that lie in respective facial planes and bound asubstantially porous internal structure 271 of the base sheet. Interioredge 272 surrounds an aperture of the gasket and the porous internalstructure is exposed on the edge. Coating 273 is disposed around theinterior edge of the base sheet and includes an edge coating 274, whichwraps onto the faces of the base sheet to form face coatings 276 and277. The coating 273 is formed of an appropriate polymeric or othersuitable material and penetrates the porous edge of the base sheet todefine an intrusion zone 278, which seals the pores, bonds the edgecoating, and stiffens or densifies the interior edge portion of the basesheet to concentrate available compression load.

For a standard 0.031 inch thick automotive gasket, the thickness of theface coatings 276 and 277 preferably is less than about 11 mils, atleast in regions of the gasket where compression failure resistance ofthe base sheet must be preserved. Further, the width of the facecoatings in these regions preferably is between about 5 mils to about0.6 inches depending upon the flange width of the gasket and in anyevent cover less than about 50 percent of the area of the base sheet.The thickness of the edge coating preferably ranges between about 1 miland about 50 mils, as required by the specific gasketing application.

The edge and face coated gasket of FIG. 22 is a good option for sealingjoints where relatively low flange pressures and/or rough, damaged,warped, or thin flange surfaces are to be encountered. In addition tothe sealing mechanisms discussed above relative to FIG. 21, the wrappededge configuration of FIG. 22 provides an additional sealing mechanismby concentrating the available clamping load on the face coatings,creating sealing forces up to 10 times higher than with non-treated orcontrolled compression rubber gaskets. Thus, a loss of even a largepercentage of the initial clamping load does not reduce the compressivestress below the level required to maintain a seal.

FIG. 23 illustrates a third embodiment that embodies the best mode ofthe present invention. In this embodiment, the edge coating is similarto that of FIG. 21 in that there is no coating on the faces of thegasket. However, the edge coating is substantially thinner and theprotruding rims beyond the facial planes are substantially shorter thanin FIG. 21. This configuration has been found advantageous for sealinghigh compression joints and/or high quality joints between rigid, flat,and smooth flange surfaces. In these types of joints, the potential forleakage due to warping, surface roughness, or compression gradients islow; however, intersticial leakage can still be a factor. Thus, theprimary sealing mechanism of the edge coating in FIG. 23 is provided bythe sealing of the exposed porous internal structure of the base sheetaround the aperture of the gasket to prevent intersticial leakage.

The gasket 281 in FIG. 23 comprises a compressible porous base sheet 282having opposed faces 283 an 284, which lie in respective facial planesand bound the porous internal structure 286 of the base sheet. Aninterior edge 287 surrounds an aperture of the gasket and the porousinternal structure of the base sheet is generally exposed on this edge.A relatively thin edge coating 288 is disposed on the edge 287 and isdeposited as described above. The material of the edge coating is chosenfor its ability to penetrate and seal the exposed pores on the edge ofthe base sheet, forming a sealed and densified intrusion zone 287 aroundthe aperture. The edge coating 288 protrudes slightly beyond the facialplanes of the base sheet to form relatively small rims that surround theaperture. The same sealing mechanisms as in the gasket of FIG. 21 areexhibited by this embodiment; however, contributions to the seal due theconforming of the edge coating to flange surface contours and roughnessare significantly less prevalent because these factors are much lesssignificant in cases of highly stressed joints with flat smooth flangesurfaces. An excellent seal against intersticial leakage is provided bythe intrusion zone, which also densifies the edge region to concentrateavailable compression force to enhance the seal even further. As withall embodiments of the invention, the material of the edge coating isselected to be substantially impervious to and chemically non-reactivewith the particular fluid to be sealed by the gasket.

FIG. 24 illustrates an edge coated gasket according to the inventionwith edge coatings on both an interior edge and the exterior edge of thebase sheet. As mentioned above, such a gasket may be advantageous whensealing against seepage of atmospheric gasses into a chamber such as,for example, in a vacuum pump or an engine's intake manifold. The gasket291 is shown poised between a pair of flanges 292 and 293, which may bebolted together with a bolt 294 and nut 296 to compress the gasketbetween the flange surfaces. Of course, the flanges shown in FIG. 24 aregreatly simplified for clarity of discussion and it will be understoodthat the gasket may in reality be compressed between mating surfaces ofvirtually any configuration, be they the surfaces of actual flanges orother components to be mounted together.

The gasket 291 comprises a compressible porous base sheet 297 havingfaces 298 and 299 that lie in respective facial planes and that boundthe porous internal structure 301 of the base sheet. The base sheet iscut or otherwise formed with an interior edge 302, which surrounds anaperture of the gasket, and an exterior edge 303, which defines theouter perimeter of *the gasket. An interior edge coating 304 is disposedon the interior edge of the base sheet and penetrates the pores of theedge to define an interior intrusion zone 306. Similarly, an exterioredge coating 307 is disposed on the exterior edge 303 of the base sheetand penetrates the pores of the exterior edge to form an exteriorintrusion zone 308.

The interior edge coating is similar to the coating of FIG. 21 and doesnot wrap to form face coatings and the exterior edge coating is similarto the coating of FIG. 22 in that the coating material wraps around theexterior edge to form face coatings. It should be understood that theillustrated combination of edge coating configurations in FIG. 24 isselected for illustration only and any combination might be chosen tosuit a particular sealing application. However, edge coated gaskets withedge coatings on both interior and exterior edges are advantageous inmany situations and are within the scope of the present invention.

FIG. 25 illustrates an alternative embodiment of the present invention.In previous embodiments, various edge coatings are presented and theintrusion of the coating material into the edge of the base sheet toform an intrusion zone is discussed. The embodiment of FIG. 25 functionsthe same as the previous embodiments in terms of its sealing mechanismsand performance. However, in this embodiment the edge coating materialitself does not penetrate the porous edge of the base sheet. Instead, aprimer or undercoat of a first material is applied to and penetrates thepores of the edge to form the intrusion zone. The edge coating is thenapplied to the primer. Such a configuration may be chosen for a varietyof reasons such as, for example, situations wherein the edge coatingmaterial and the material of the gasket are chemically incompatible ordo not bond well to each other. The embodiment of FIG. 25 is a solutionand is intended to be encompassed within the scope of the presentinvention.

Referring in more detail to FIG. 25, an edge coated gasket 311 has abase sheet 312 of compressible gasket material with faces 313 and 314bounding the fibrous internal structure 316 of the gasket. An interioredge 317 of the base sheet defines an aperture of the gasket. Anundercoating of primer 318 is applied to the interior edge 317 andpenetrates and seals the pores on the edge to form an intrusion zone320. The primer is thus securely bonded to the edge coating and forms adensified intrusion zone, which concentrates compression forces andenhances the seal provided by the gasket.

An edge coating 319 is applied as discussed above to the undercoating ofprimer and is formed with one of the generally preferred profiles ofthis invention. The primer is selected to be chemically compatible withand to penetrate and adhere to the edge of the gasket and also toprovide a layer with which the edge coating material is compatible andto which the edge coating material adheres. Thus, it is seen that theoverall modes of functionality of the edge coated gasket 311 issubstantially the same as the previously discussed embodiments, exceptthat an undercoat of primer material is disposed between the edgecoating and the edge of the base sheet and it is the primer materialthat forms the intrusion zone rather than the edge coating material.

The present invention and the many advantages thereof as well as thefoundation for some of the design parameters discussed herein may beunderstood better from the following examples and results of testsperformed on edge coated gaskets fabricated according to the invention.The tests were performed, in part, to quantify and determine realisticlimits for many of the design parameters, such as, for example,preferred thickness and width of face coatings. However, these examplesare included to illustrate and clarify the invention and not to limitthe invention.

EXAMPLES Example 1

A. Crush Test—ASTM F1574-95

In this example, a crush test was performed on gasket samples preparedin accordance with the present invention using test standard ASTMF1574-95, which is an industry standard for testing the compressionstrength of a gasket under elevated temperatures. Each gasket wassubjected to a controlled amount of flange pressure at 300 degreesFahrenheit under uniform load conditions. The deformation of the sampleas a percentage increase in surface area over the original gasketsurface area was then measured. To prepare test gaskets, identicalannular gaskets were cut from a cellulose-based paper gasket sheetmaterial. Each gasket included upper and lower opposing faces, aninterior edge defining an aperture, and an outer peripheral edge. Thegaskets had an inner diameter of 0.515 inches, an outer diameter 0.950inches, and a resulting flange width of 0.2175 inches.

Table 1 shows the results of the crush test in terms of the change ingasket area as a function of flange pressure. The results for acompletely uncoated gasket, i.e. a gasket with no edge or face coatings,are shown in column A and serve as the control. Column B contains thetest results for a gasket having an NBR latex coating on the interioredge of the gasket. Column C contains the test results for a gasket withan NBR latex coating on its interior edge and a face coating of a secondmaterial formed on each face and extending in a strip surrounding theaperture of the gasket. The face coatings contact the NBR latex edgecoating as illustrated in FIG. 2. The face coatings on the sample were 4mils thick and were ⅛ inch wide, measured radially outwardly from theinterior edge of the gasket. Thus, the face coatings in this testcovered approximately 50 percent of the area of each face. Column Dcontains results for a gasket having a coating over its entire surfaceof a room temperature vulcanizable silicone from Loctite Corp. In thisexperiment, a change in gasket surface area greater than 10 percent isdeemed indicative of compression failure and is considered unacceptable.The higher the number, the worse the compression failure resistance andthe more undesirable the gasket.

TABLE 1 Percentage Change In Gasket Surface Area As a Function of FlangePressure Pressure PSI A B C D 2500 − − −  2 3250 − − − 21 5000 − − 1 6010,000 2 1 9 −− 15,000 2 4 35 −−

The above data demonstrate that an untreated gasket alone (column A)exhibits exceptional compression failure resistance at all flangepressures. On the other end of the spectrum, a gasket having a coatingon its entire surface (column D) experiences compression failure even ata relatively low flange pressure of 3250 PSI. It is clear, then, thatcoatings on the faces of a gasket deteriorate significantly thecompression failure resistance of the gasket. However, the data alsodemonstrate that edge coated gaskets according to the present invention(column B) have a minimum impact on compression failure resistance,exhibiting a surface area change of far less than 10%, even under aflange pressure of 15,000 PSI. In fact, the edge coated gasket in thistest exhibited compression failure resistance almost as good as the bareuncoated control gasket (column A). The results shown in column Cdemonstrate that a gasket having both an edge coating and a face coatingextending in a relatively narrow strip around the gasket apertureexhibits slightly more degraded compression failure resistance, showingunacceptable results above a flange pressure of 10,000 PSI.

The overall conclusion to be drawn from this test is that uncoatedgaskets exhibit excellent compression failure resistance. Coatings, andparticularly face coatings, on the gasket degrade this compressionfailure resistance by an amount proportional to the percentage of face'ssurface area covered by the face coating. Gaskets with face coatingscovering 50 percent of the facial areas of the gasket result incompression failure above flange pressures of about 10,000 PSI. Thus,face coatings on gaskets of the present invention should cover less thanabout 50 percent of the facial area of the gasket and preferably lessthan about 30 percent. Gaskets with completely coated faces exhibitcompression failure even at low flange pressures and generally areunacceptable.

B. Sealability Test

Three groups of standard EMALT gaskets (A, B, and C) having innerdiameters of 2.5 inches and outer diameters of 3.75 inches were preparedas described above. The face coatings for the gaskets in column C were{fraction (3/16)} inch wide. Thus, the face coatings on these gasketscovered approximately 26 percent of the areas of the gasket faces.

Each of the gasket samples was clamped between the flanges connectingtwo halves of a test cylinder and the cylinder was pressurized withnitrogen after tightening the flanges to obtain the flange pressuresindicated in Table 2. The test was performed using a smooth flange withmating surfaces measuring 18 Ra, where Ra is the average roughness valuemeasured in micro-inches, and on a rough flange having mating surfacesmeasuring 250 Ra. The cylinder was pressurized with nitrogen to aninternal pressure of 14 PSI. The elapsed time until the pressure withinthe cylinder decayed to 13 PSI was measured as noted in Table 2.

TABLE 2 Sealability As a Function of Gasket Type and Flange RoughnessFlange Characteristics Gasket Time (min) Flange Pressure Roughness A 1.5 2100 PSI  18 Ra A  1.0 2100 PSI 250 Ra B 11.0 2100 PSI  18 Ra B11.0 2100 PSI 250 Ra C Total Seal  300 PSI  18 Ra C Total Seal  300 PSI250 Ra

The uncoated control gasket A resulted in relatively high leakage timesof between 1 and 1.5 minutes. It is thus clear that bare uncoatedgaskets do not provide exceptional. sealability at the tested flangepressures. An edge coated gasket (gasket B),exhibits roughly a 10 foldimprovement in sealability over the control gasket. However, asillustrated by the data for gasket type C (gaskets with both an edgecoating and face coatings), a total seal is obtained, i.e. no measurableleakage is noted either for smooth or rough flanges, even at anextremely low flange pressure of 300 PSI. It is concluded from this testthat in applications where outstanding sealability is required evenunder very low flange pressures, a gasket with both an edge coating andface coatings are preferable. This test, in conjunction with the resultsof the crush test of Example 1, leads to the conclusion that facecoatings to enhance sealability should cover less than about 50% of agaskets face and more preferably less than about 30% in order topreserve the compression failure resistance of the gasket material.Judicious selection of the width of face coating strips providessimultaneously both outstanding sealability and compression failureresistance. This test also demonstrates that a bare uncoated gasketleaks significantly under flange pressures as high as 2100 PSI. A gasketwith only an edge coating seal performs significantly better than a baregasket, but still provides less than a total seal. Gaskets with bothedge and face coatings provide total seals under the conditions of thistest.

Example 2

In the test of this example, the sealability effectiveness of edgecoatings was measured. Identical gasket base sheets were obtained fromthe same gasket sheet material. Each gasket included opposed faces andan interior edge surrounding and defining an aperture of the gasket.Gasket A was left completely uncoated and represents the control in thistest. A second gasket, gasket B, was provided with an edge coating onlyon the interior edge of the base sheet. The edge coating comprised acommercially available NBR latex material.

A high-pressure sealability test was performed on gaskets A and B. Thegaskets were placed between the flanges connecting two halves of thecylinder and the flanges were tightened to compress the gaskets with theindicated flange pressures. The cylinder was then pressurized withnitrogen to a pressure of 225 PSI for one hour. The pressure remainingin the cylinder after one hour was then measured and noted as indicatedin the chart below. Gaskets with highest sealability are evidenced bythe highest residual pressure in the cylinder after one hour. Table 3shows the results of the test.

TABLE 3 Sealability of Gaskets Flange Pressure (PSI) Gasket 500 1000 Auncoated gross leak gross leak B coated 218 PSI 223 PSI

Gasket A with no coating exhibited such a gross leak that it was notpossible in this test to determine the residual gas pressure after onehour. Thus, bare uncoated gaskets provide unacceptable sealability, atleast for relatively low flange pressures between 500 and 1000 PSI.However, providing an edge coating on the interior edge of the gasketbase sheet (gasket B) results in a gasket with drastically improvedsealability at these low flange pressures. Even at the lower flangepressure of 500 PSI, the edge-coated gasket held the gas pressure at 218PSI at the conclusion of one hour, thus loosing only 7 PSI. Thus, it maybe concluded that providing an edge coating on a gasket base sheetresults in a gasket that exhibits exceptional sealability at low flangepressures where an uncoated gasket alone is unacceptable.

Example 3

In this test, the same gaskets tested for sealability in Example 2, weresubjected to the crush test described in Example 1. Uncoated gasket Aserved as the control. Gasket B was provided with an edge coating asdescribed. The two gaskets were then subjected to the crush testdescribed above. The results of the test, in units of percent change insurface area of the gaskets, are outlined in Table 3.

TABLE 4 Percentage Area Change as a Function of Flange Pressure Gasket5,000 PSI 10,000 PSI 15,000 PSI A uncoated 1 10 16 B edgecoated 2 9 16

The results of this test demonstrate that the edge coated gasket, whichdemonstrates exceptional sealability as shown in Example 2, alsoexhibits compression failure resistance substantially unchanged from abare uncoated gasket (gasket A). Compression failure resistance of thetwo was the same at 15,000 PSI flange pressures. Conclusions to be drawnfrom this example in conjunction-with the test of Example 2 are thatedge coated gaskets according to the present invention provide both highcompression failure resistance and exceptional sealability under a widerange of flange pressure conditions from 500 PSI to 15,000 PSI. This isa significant improvement over bare uncoated gaskets, which showvirtually no sealability at lower flange pressures and reducedsealability even at higher flange pressures.

Example 4

In this example, gaskets according to the present invention were testedfor sealability when compressed between flanges that are warped, i.e.that have flange surfaces that vary from flat. These conditions can anddo occur in the real world for a variety of reasons and, when present,can result in a joint with serious sealability problems using prior artgaskets. In this test, a warped flange was simulated by deforming thetest flange of the aforementioned pressure cylinder into a slightlyconcave shape. The concavity, or deviation from flat, of the test flangemeasured 3 mils at a central portion of the flange, which wasapproximately 1.42 inches in diameter. The warped flange was then fittedin turn with a gasket A (an uncoated control gasket) and a gaskets C (agasket with both an edge coating and face coatings). The flange boltswere torqued to 13.5 foot-pounds and the cylinder was filled with oiland pressurized with air to 5 PSI.

Leakage of oil across the flanges was measured after an elapsed time of46 hours. Intersticial and/or interfacial migration of oil acrossgreater than ⅔ of the width of the flanges was considered in this testto indicate gasket failure. The results of the test were as follows.With gasket A (the uncoated control gasket) the oil migrated completelyacross the width of the flanges and leaked to the outside of the testcylinder after 46 hours. Obviously, the uncoated gasket failed toprovide a seal under warped flange conditions. However, gasket C, withedge and face coatings, resulted in no migration of oil either throughthe gasket material or between the gasket and the flange surfaces after46 hours. In other words, the edge and face coated gasket in this testprovided a perfect seal under warped flange conditions. A conclusion tobe reached from this test, therefore, is that gaskets with an edgecoating and face coating covering less than 30% of the area of thegasket face according to the present invention, provide exceptionalsealability even when used with flanges having warped mating surfaces.

As illustrated in Example 1, such gaskets also provide exceptionalsealability when used with flanges having rough or damaged flangesurfaces. It is suspected that this advantageous property results fromthe fact that the edge coating material tends to fill any imperfectionsor roughness in the flange surfaces and also tends to conform to gradualwarpage or other deviations from flat of the flange surfaces. Adhesionbetween the coating material and the flange surfaces also is thought tocontribute to the exceptional performance demonstrated by gaskets of thepresent invention.

Example 5

In this example, an annular gasket base sheet having the dimensionsdescribed in Example 2 was cut from a standard fibrous gasket material.The interior edge of the base sheet was coated with a commercial acryliclatex coating. The coating was applied to the interior edge of the basesheet and projected beyond the facial planes of the base sheet to formraised rims extending around the aperture of the gasket. Further, theedge coating had a rounded inner surface and was thicker in its centralportion than around its rim portions. The thickness of the base sheetwas about 32 mils and the raised rims of the edge coating protrudedapproximately 27 mils beyond the facial planes of the base sheet. Inthese aspects, the edge coating of this example resembled the edgecoating illustrated in FIG. 5.

The gasket was tested by clamping it between the flanges of the testcylinder described above. Flanges having smooth flange surfaces (18 Ra)were used. The cylinder was pressurized with Nitrogen to 14 PSI and thenumber of minutes until the pressure decayed to 13 PSI was measured andnoted. The results for gasket A in Example 2 above were used as thecontrol. The results of this test are as follows. The uncoated controlgasket allowed the pressure within the cylinder to decay to 13 PSI in amere 1.5 minutes and required a relatively high flange pressure of 2100PSI. As discussed above, this is considered unacceptable performance.However, the edge coated gasket in this test provided a total seal, i.e.no loss of pressure was measurable, even at flange pressures as low as300 PSI.

Conclusions to be drawn from the results of this test and the othertests are that uncoated prior art fibrous gaskets generally provide poorsealability at flange pressures of about 2100 PSI, even though theygenerally exhibit good compression failure resistance. In contrast, anedge coated gasket formed with raised protruding rims according to thepresent invention delivers near perfect to perfect sealability even atlow flange pressures of about 300 PSI. The test of Example 1demonstrates that such edge coated gaskets also deliver very goodcompression failure resistance, in part because no portion of the facesof the gasket base sheet are coated. Thus, edge coatings with projectingrims such as those illustrated in FIGS. 5, 9, 12, 14, 17, and 21 provideexcellent sealability similar to that provided by edge and face coatedgaskets while at the same time preserving virtually all of thecompression failure resistance inherent in gasket material of the basesheet.

Example 6

For the test of this example, an annular gasket base sheet with thedimensions discussed in Example 1 was cut from a commercial fibrousgasket material. A silicone edge coating was applied to the interioredge of the base sheet with a cross-sectional profile resembling theedge coating shown in FIG. 6. More specifically, the edge coatingoverlapped onto one face of the base sheet to form a face coatingextending in a strip around the aperture of the gasket. The edge coatingwas approximately 100 mils thick at the center of the interior edge ofthe base sheet and the face coating covered less than 30% of the surfaceof the face. The edge coated gasket was tested between the flanges ofthe test cylinder pressurized with nitrogen to 14 PSI. The elapsed timeuntil the pressure decayed to 13 PSI was measured and noted. Smoothsurfaced flanges (18 Ra) were used in this test and the results fromExample 2 for gasket A (uncoated gasket) were used as the control.

The control gasket resulted in a decay time to 13 PSI of 1.5 minutes ata flange pressure of 2100 PSI. In contrast, the edge coated gasket inthis test provided total sealability (the pressure never measurablydecreased in the cylinder) at the same flange pressure of 2100 PSI.Thus, at least at flange pressures above 2100 PSI, an edge coated gasketwith a face coating strip on one face provided superior sealability ascompared to uncoated gaskets. Further, as can be seen from the test ofExample 1, such edge coated gaskets also substantially preserve the goodcompression failure resistance of the gasket material of the base sheet.Thus, overall gasket performance is substantially enhanced with gasketsof the present invention.

Example 7

In the test of this example, an edge coated gasket resembling that ofFIG. 8 was tested for sealability. An annular gasket with a siliconeedge coating was fabricated. The edge coating wrapped around onto bothof the faces of the gasket base sheet to form face coatings thatextended in a strip around the aperture of the gasket. The face coatingscovered less than 30 percent of the faces of the base sheet. The edgecoated gasket was tested with the smooth flanged (18 Ra) test cylinderpressurized with nitrogen to 14 PSI. Elapsed time until the pressuredecayed to 13 PSI was measured and noted. Gasket A of Example 2 was usedas the control. The control gasket resulted in a decay time to 13 PSI of1.5 minutes and required a flange pressure of 2100 PSI. The edge coatedgasket provided a total seal (pressure never measurably decreased in thecylinder) at a substantially lower flange pressure of 300 PSI. Thus,silicone edge coated gaskets with overlapping face coatings coveringless than 30 percent of the faces of the gasket base sheet provideexceptional sealability without significantly degrading the compressionfailure resistance of the base sheet.

Example 8

As discussed above, providing gaskets with coatings, and particularlyface coatings, to increase sealability degrades the gasket's ability toresist compression failure. In general, the greater the facial surfacecovered by a coating, and the greater the coating's thickness, the lowerthe gasket's resistance to compression failure. It therefore isimportant to limit the width as well as the thickness of face coatingsas much as possible while still obtaining the substantially enhancedsealability provided by such coatings. The test of this example isdesigned to explore the effect of face coating thickness and width oncompression failure resistance.

For this test, identical annular gaskets were cut from a commerciallyavailable fibrous gasket sheet material. Nine specimens, specimens Athrough I, were then prepared for the test by applying different edgeand face coatings to the gaskets as outlined in more detail below.Specimen A was left uncoated and was used as the control in this test.The specimens were then subjected to the crush test as outlined inExample 1 above to determine the effect the coatings in each sample onthe compression failure resistance of the gasket.

Gasket B was provided with an edge coating with projecting rimsprotruding beyond the facial planes of the base sheet. No face coatingswere present on this gasket. The edge coating profile for gasket Bresembled the coating illustrated in FIG. 5. Gasket C was provided withface coatings extending in strips around the aperture of the gasket butwas not provided with an edge coating. Each of the face coatings wasmeasured to be from 3.2 to 4.2 mils in thickness and was 92 mils wide,as measured radially outward from the interior edge of the gasket basesheet. Gasket D was provided with a face coating on a portion of eachface of the gasket with each face coating being from about 0.8 to about1.2 mils in thickness and 92 mils wide, as measured radially outwardfrom the interior edge of the gasket's base sheet. As with gasket C,gasket D was not provided with an edge coating on the interior edge ofthe base sheet. Gasket E also was provided with a face coating coveringa portion of each face of the gasket. Each face coating was measured tobe between about 3.2 and about 4.2 mils in thickness and was 188 milswide, as measured radially outward from the interior edge of the basesheet. As with gaskets C and D, gasket E did not include an edgecoating. Gasket F was provided with a face coating on each face that wasmeasured to be from about 0.8 to about 1.2 mils in thickness and thatwas 188 mils wide, as measured radially outward from the interior edgeof the base sheet. No edge coating was applied. Gasket G had a facecoating on each face of the gasket that was from about 3.2 to about 4.2mils in thickness and 282 mils wide, as measured radially outward fromthe interior edge of the gasket. No edge coating was applied. Gasket Hwas provided with a face coating on each face of the gasket thatmeasured from about 0.8 mils to about 1.2 mils in thickness and that was282 mils wide, as measured radially outward from the interior edge ofthe gasket. No edge coating was applied. Gasket I was provided atraditional release coating on each face of the gasket. The releasecoating was approximately 1 mil thick and covered the entire surfacearea of each face.

None of the coated gaskets for this test were provided with edgecoatings. This is because it is known from other tests that edgecoatings alone without any face coatings have little or no effect on thecompression failure resistance of gaskets. The goal of the present testwas to quantify the compression failure resistance of gaskets as afunction of face coating width and thickness. Edge coatings wereeliminated to isolate these parameters and to remove from the test anycontribution, however small, from an edge coating.

The crush test in this example was conducted for each gasket at atemperature of 300 degrees Fahrenheit as specified by ASTM F1574-95. Thetest results are stated in terms of percentage change in a gasket'ssurface area from its original surface area before the test. The greaterthe change in surface area, the greater the compression of the gasketand the worse its compression failure resistance. As with the test ofExample 1, a surface area change of greater than 10 percent isindicative of an unacceptable condition and is evidence that a gasketwould exhibit unacceptable compression failure resistance. In general,the lower the change in surface area, the better the gasket will resistcompression failure under actual conditions. The results of the test aretabulated below in Table 5.

TABLE 5 Compression Failure As A Function of Gasket Type and FlangePressure Sample 7500 PSI 10000 PSI 12500 PSI 15000 PSI 20000 PSI A 1.542.13 2.20 4.38 B 2.13 2.33 3.53 3.59 4.57 C 3.76 5.42 6.28 9.53 19.51 D2.47 3.59 3.73 6.84 14.51 E 8.82 14.32 16.85 28.01 42.98 F 2.35 5.987.79 15.49 35.00 G 12.76 20.84 33.72 41.50 100.00 H 1.98 5.62 12.2631.81 43.66 I 0.56 1.03 1.60 3.16 3.54

One notable conclusion to be drawn from this data is that traditionalrelease coatings on the faces of a gasket (gasket I) have little if anyeffect on the compression failure resistance of the gasket. As discussedhereinabove, these are coatings that are very thin and do not tend topenetrate the material of the gasket. In general, however, the dataresulting from this test show that compression failure resistance variesas a function of flange pressure and as a function of the thickness andwidth of a face coating (other than a release coating) on the faces of agasket.

The control gasket, gasket A, demonstrated good compression failureresistance at all flange pressures, as expected. Gasket B showedacceptable compression failure resistance at flange pressures of 20,000PSI and below. Gasket C showed acceptable resistance at 15,000 PSI andbelow as did gasket D. Gasket E showed acceptable compression failureresistance at 7,500 PSI and below while gasket F showed acceptableperformance at 12,500 PSI and below. Gasket G demonstrated unacceptablecompression failure resistance at all flange pressures and gasket Hshowed acceptable performance only up to a 10,000 PSI flange pressure.Conclusions to be drawn from this test are that compression failureresistance indeed is a strong function of the application of facecoatings, and particularly the width and thickness of such facecoatings, on gasket base sheets. Face coatings covering less than 50percent of the surface area of a gasket's face are preferred, withcoverage less than 30 percent being most preferable, to providesealability and compression failure resistance simultaneously.

Example 9

For the test of this example, two identical annular gaskets were cutfrom a cellulose-based paper gasket sheet material. Each gasket had abase sheet formed to define an interior aperture surrounded by aninterior edge of the base sheet. The gaskets for this test each had aninner diameter of approximately 0.515 inches, and outer diameter ofapproximately 0.95 inches (for a flange width of approximately 0.2175inches), and a thickness of {fraction (1/32)} inches (or 0.031 mils).Gasket A was left completely uncoated and was used as the control.Gasket B was provided with an edge coating made of an acrylic latexcoating material. No face coatings were applied to the gasket faces. Theedge coating was wider than the thickness of the gasket base sheet andprotruded beyond the facial planes of the base sheet on each side todefine projecting rims surrounding the aperture of the gasket. Theprojecting rims were measured to protrude beyond the facial planes ofthe gasket by approximately 27 mils on each side. The thickness of theedge coating at approximately the mid portion of the interior edge ofthe base sheet was measured to be approximately 0.9 millimeters. Theprofile of the edge coating was similar to that shown in FIGS. 5 and 23.

Gaskets A and B were tested using the test cylinder pressurized withnitrogen to a pressure of 14 PSI and with the smooth flange (18 Ra). Theelapsed time until the pressure decayed to 13 PSI was measured andnoted. The control gasket, gasket A, resulted in a decay time of 1.5minutes and required a flange pressure of 2100 PSI. Gasket B obtained atotal seal (pressure never decreased measurably in the cylinder) at aflange pressure of 300 PSI. This test further demonstrates theexceptional qualities of edge coated gaskets made according to thepresent invention to provide outstanding sealability even at low flangepressures while at the same time preserving the compression failureresistance of the gasket base material.

While preferred embodiments of the gasket of this invention andpreferred methodologies have been illustrated and described above, itwill be appreciated that many variations of these embodiments arepossible within the scope of the invention. Therefore, while theinvention has been disclosed in preferred forms only, it will be obviousto those skilled in the art that no undue limits should be imposed onthe invention except as set forth in the claims hereof. For example, itis contemplated that a cross-sectional profile of an edge and/or facecoating according to the invention may take on a multitude of shapes andsizes other than those discussed herein and illustrated in the drawings,so long as the fundamental attributes of sealability and compressionfailure resistance are preserved. Furthermore, the list of possiblecoating materials provided herein is in no way exhaustive, and it iscontemplated that other substances and materials, now known or to bediscovered, may be suitable for fulfilling the requirements of an edgeor face coating of the invention. These and other additions, deletions,and modifications may well be made to the preferred embodimentsdisclosed herein without departing from the spirit and scope of theinvention as set forth in the claims.

What is claimed is:
 1. A gasket comprising: a base sheet of contiguoussubstantially porous gasket material having a predetermined thicknessand two opposed substantially parallel and exposed faces for contactingrespective flange surfaces between which said gasket is to be clamped;said base sheet being configured to define at least one aperture boundedby an interior edge of said base sheet; an edge coating disposed on saidinterior edge of said base sheet, said edge coating being formulated andconfigured to provide an enhanced seal when said gasket is compressedbetween a pair of flange surfaces, said edge coating penetrating saidinterior edge to form an intrusion zone of said base sheet surroundingsaid aperture, said intrusion zone having a width, said edge coatinghaving a thickness in a direction transverse to said interior edge ofsaid base sheet; said edge coating penetrating said interior edge asufficient distance such that said width of said intrusion zone is atleast twice said thickness of said edge coating, the region of said basesheet within said intrusion zone being denser as a result of saidpenetrating edge coating than regions of said base sheet outside saidintrusion zone to enhance clamping pressure in said intrusion zone whensaid gasket is clamped between a pair of flange surfaces.
 2. A gasket asclaimed in claim 1 and wherein said edge coating is a polymeric coating.3. A gasket as claimed in claim 1 and wherein said edge coating is alatex coating.
 4. A gasket as claimed in claim 1 and wherein said edgecoating is a powder fused coating.
 5. A gasket as claimed in claim 1 andwherein said opposed faces lie in respective spaced apart facial planesand wherein said edge coating has edge portions adjacent said facialplanes, a central portion intermediate said facial planes, a thicknessin a direction substantially parallel to said facial planes, and a widthin a direction substantially transverse to said facial planes.
 6. Agasket as claimed in claim 5 and wherein said thickness of said edgecoating is substantially the same throughout said width of said edgecoating.
 7. A gasket as claimed in claim 5 and wherein said edge coatinghas a width substantially the same as said predetermined thickness ofsaid base sheet, said edge portions of said edge coating substantiallylying within said facial planes within which said exposed faces lie. 8.A gasket as claimed in claim 5 and wherein at least one of said edgeportions of said edge coating protrudes beyond its respective facialplane to define a protruding rim.
 9. A gasket as claimed in claim 8wherein each of said edge portions of said edge coating projects beyondits respective facial plane to define spaced apart protruding rimsdisposed on either side of said base sheet.
 10. A gasket as claimed inclaim 1 and further comprising a release coating on at least one of saidfaces to enhance removal of said gasket after use.
 11. A gasket asclaimed in claim 2, wherein said polymeric coating is selected from agroup consisting essentially of: acrylic, acrylonitrile, acrylonitrilebutadiene rubber, fluoro polymers, hydrogenated acrylonitrile butadienerubber, styrene butadiene polymer, fluoroelastomer polymer,acrylic-acrylonitrile polymers, carboxylated acrylonitrile polymer,carboxylated styrene butadiene polymer, polyvinylidene chloride,chloroprene rubber polymer, ethylene propylene rubber polymer,ethylene/vinyl acetate polymer, epoxy, fluorosilicones, polyurethane,and silicone rubber coatings and mixtures thereof.
 12. A gasket asclaimed in claim 1 and wherein said edge coating is an inorganic/organichybrid.
 13. A gasket comprising a base sheet of compressible gasketmaterial having a predetermined thickness and spaced apart substantiallyparallel exposed faces lying in respective facial planes, said exposedfaces for engaging respective flange surfaces between which said gasketis to be clamped, said base sheet being configured to define an interioraperture bounded by a substantially porous interior edge of said basesheet, said interior edge extending between said facial planes, and anedge coating formed on said interior edge of said base sheet and havinga thickness in a direction parallel to said facial planes, said edgecoating extending at least partially around said aperture andpenetrating said substantially porous edge a distance at least twice thethickness of said edge coating to form an intrusion zone surroundingsaid interior aperture and having a width at least twice the thicknessof said edge coating, said intrusion zone bonding said edge coating tosaid interior edge and increasing the relative density of said basesheet within said intrusion zone thereby enhancing clamping pressurewithin said intrusion zone when said gasket is clamped between a pair offlange surfaces.
 14. A gasket as claimed in claim 13 and wherein saidedge coating has a thickness in a direction substantially parallel tosaid facial planes and a width in a direction substantially transverseto said facial planes.
 15. A gasket as claimed in claim 14 and whereinsaid width of said edge coating is greater than said predeterminedthickness of said base sheet, said edge coating protruding beyond atleast one of said facial planes to define a protruding rim relative tosaid exposed face lying in said facial plane, said protruding rimextending at least partially around said aperture.
 16. A gasket asclaimed in claim 15 and wherein said edge coating protrudes beyond eachof said facial planes to define a first protruding rim relative to oneof said exposed faces and a second protruding rim relative to the otherone of said exposed faces, said first and second protruding rimsextending at least partially around said aperture.
 17. A gasket asclaimed in claim 14 wherein said thickness of said edge coating issubstantially uniform across said width of said edge coating.
 18. Agasket comprising: a base sheet of gasket material having exposed faceslying in respective spaced apart facial planes and an interior edge thatsurrounds and defines an aperture; an edge coating disposed on saidinterior edge of said base sheet, said edge coating having a thicknessin a direction substantially parallel to said facial planes; said edgecoating penetrating said interior edge to form an intrusion zone of saidbase sheet around said aperture and projecting beyond at least one ofsaid facial planes to define a rim extending at least partially aroundsaid aperture, said intrusion zone having a width at least twice thethickness of said edge coating and a density greater than the density ofsaid base sheet outside said intrusion zone to enhance clamping pressurewithin said intrusion zone when said gasket is clamped between a pair offlange surfaces.
 19. A gasket as claimed in claim 18 and wherein saidedge coating projects beyond each of said facial planes to form opposedrims that extend at least partially around said aperture.